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Errors and approximations - class-XII

Description: errors and approximations
Number of Questions: 56
Created by:
Tags: applications of derivatives application of derivatives - i maths application of derivatives the trapezium rule
Attempted 0/56 Correct 0 Score 0

The approximate value of $\sqrt[10]{0.999}$ is 

  1. 0.0998

  2. 0.9998

  3. 0.0999

  4. 0.9999


Correct Option: A

The positive root of ${x}^{2}-98.8=0$ after first approximation by Newton Raphson method assuming initial approximation to the root is $14$ is

  1. $9.821$

  2. $9.814$

  3. $9.715$

  4. $9.915$


Correct Option: B
Explanation:

Here ${x} _{0}=14, f(x)={x}^{2}-78.8$
and $f'(x)=2x$
$\therefore$ ${x} _{1}={x} _{0}-\cfrac{f({x} _{0}}{f'({x} _{0})}$
$=14-\cfrac { { \left( 14 \right)  }^{ 2 }-\left( 78.8 \right)  }{ 2\times 14 } =9.814$

State the following statement is True or False

According to the Newton-Raphson's method the approximate root of the equation $f(x) = 0$ is $x _{n}$ then be $x _{n} = x _{n + 1} - \dfrac {f(x)}{f'(x _{n})}$.

  1. True

  2. False


Correct Option: B
Explanation:
If $x _n$ is the approximate root of $f(x)=0$ then the value of $x _n$ given by Iterative eqn. for Newton-Raphson method is 
    ${ x } _{ n+1 }= { x } _{ n } - \dfrac { f({ x } _{ n }) }{ f' ({ x } _{ n }) } $, where $f'(x _n)$ is derivative of $f$ at $x _n$

$\therefore $ The given statement is FALSE.

The value of $\cdot23454\ E\ 06 +\cdot31063\ E06.$ is?

  1. $ \cdot54517\ E\ 06$

  2. $\cdot12057\ E\ 09$

  3. $\cdot12057\ E\ 05$

  4. $\cdot64045\ E\ 09$


Correct Option: A
Explanation:
$E06$ can be taken out common 
$= (.23454+.31036)E06$
$ = (.54517)E06 $

The value of $\cdot6235\ E\ 05 +\cdot5781\ E05.$ is?

  1. $\cdot13056\ E\ 09$

  2. $\cdot12057\ E\ 09$

  3. $\cdot64045\ E\ 05$

  4. $\cdot12057\ E\ 05$


Correct Option: C
Explanation:
Taking $E 05$ common, we get
$ = (.06235+0.5781)E05 $
$ = (.64045)E05 $

The value of $\cdot4136\ E\ 05 +\cdot5132\ E07.$ is?

  1. $\cdot517336\ E\ 07$

  2. $\cdot164045\ E\ 09$

  3. $\cdot12057\ E\ 07$

  4. $\cdot33715\ E\ 01$


Correct Option: A
Explanation:
Take out $E07$ common to get 
$= (.004136+.5132)E07$
$ = .517336E 07$

The value of $\cdot3656\ E\ 06 -\cdot7326\ E05.$ is?

  1. $\cdot12057\ E\ 09$

  2. $\cdot6423\ E\ 05$

  3. $\cdot12057\ E\ 08$

  4. $\cdot29234\ E\ 06$


Correct Option: D
Explanation:
Take out $E06$ common to get 
$= (.3456-.07326)E06 $
$ = .29234 E 06$

The value of $\cdot2642\ E\ 05 +\cdot3781\ E05.$ is?

  1. $\cdot12057\ E\ 05$

  2. $\cdot54517\ E\ 05$

  3. $\cdot6423\ E\ 05$

  4. $\cdot64045\ E\ 05$


Correct Option: C
Explanation:

$E05$ can be taken out common. 

Therefore we have 
$= (.2642+.3781)E05 $

$ = .6423E05 $

The value of $\cdot6321\ E\ 08 +\cdot5736\ E08.$ is?

  1. $\cdot12057\ E\ 05$

  2. $\cdot12057\ E\ 09$

  3. $\cdot64045\ E\ 09$

  4. $\cdot54517\ E\ 09$


Correct Option: B
Explanation:

$E08$ can be taken common 

$ = (.6321+.5736)E08 $
$ = (1.2057)E08$
$ = (0.12057)E09$

Find the approximate error in the volume of a cube with edge $x$ cm, when the edge is increased by $2\%$

  1. $4\%$

  2. $2\%$

  3. $6\%$

  4. $8\%$


Correct Option: A
Explanation:

in a mutiplication while multiplying we have to add the percentage errors 


so if the edge of the cube is $x$cm then the volume will be ${ x }^{ 3 }$

but for errors we have to add the percentage 

therefore the total error  percentage now becomes $6\%$

therefore the error is increased by $4\%$

If the length of cylinder is measured to be $4.28 cm$ with an error of $0.01 cm$, the percentage error in the measured length is nearly

  1. $0.4\% $

  2. $0.5\% $

  3. $0.2\% $

  4. $0.1\% $


Correct Option: C
Explanation:
Given:Length of the cylinder $=l=4.28\,cm$
Error$=\Delta l=0.01\,cm$
Percentage error$=\dfrac{\Delta\,l}{l}\times 100$
$=\dfrac{0.01}{4.28}\times 100=0.234\approx\,0.2\%$

The radius of the sphere is measured as $ \left( {10 \pm 0.02} \right)cm$. The error in the measurement of its volume is 

  1. $25.1 cc$

  2. $25.21 cc$

  3. $2.51 cc$

  4. $251.2 cc$


Correct Option: D
Explanation:

Let $r$ be the radius of the sphere.


$\Rightarrow$  $r=10$


Error in the measurement of radius $=\Delta r$

$\therefore$  $\Delta r=0.02\,m$

$\Rightarrow$  Volume of the sphere $(V)=\dfrac{4}{3}\pi r^3$

We need to find error in calculating the volume that is $\Delta V$

$\Delta V=\dfrac{dv}{dr}\times \Delta r$

         $=\dfrac{d\left(\dfrac{4}{3}\pi r^3\right)}{dr}\times \Delta r$

         $=\dfrac{4}{3}\pi\dfrac{d(r^3)}{dr}\times \Delta r$

         $=\dfrac{4}{3}\pi(3r^2)\times (0.0.2)$

         $=4\pi r^2\times 0.02$

         $=4\times 3.14\times (10)^3\times 0.02$

         $=251.2\,cm^3$ i.e. $251.2\,cc$

What is the sum of the factors of 496 ? 

  1. 990

  2. 996

  3. 992

  4. 985


Correct Option: C
Explanation:

The factors of $496$ are $1, 2, 4, 8, 16, 31, 62, 124, 248,496$


The sum of the factors is $1+ 2+ 4+ 8+ 16+ 31+ 62+ 124+ 248+496=992$

If there is an error of $k%$ in measuring the edge of a cube, then the percent error in estimating its volume is

  1. $k$

  2. $3k$

  3. $\displaystyle \frac{k}{3}$

  4. none of these


Correct Option: B
Explanation:

Volume of cube$V=x^{3}$
$\displaystyle \frac{dV}{dx}=3x^{2}$
Percentage error in measuring side $= k%$
$\displaystyle \Rightarrow \frac{\delta x}{x}=\frac{k}{100}$
$\displaystyle {\delta{x}}=\frac{xk}{100}$
Approximate error in estimating volume $=dV=(\frac{dV}{dx}){\delta x}=3x^{2}\frac{xk}{100}$
Percentage error in estimating volume$=\frac{dV}{V}\times 100=3k$

The height of a cylinder is equal to the radius. If an error of $\alpha$ % is made in the height, then percentage error in its volume is

  1. $\alpha$ %

  2. $2\alpha$ %

  3. $3\alpha$ %

  4. none of these


Correct Option: C
Explanation:
Volume of cylinder $V= \pi { r }^{ 2 }h$
Since, $h=r$
$V=\pi {h}^{3}$ 
$\displaystyle \dfrac{dV}{dh}=3\pi h^{2}$
Given, percentage error in measuring height $=\alpha$%
$\Rightarrow \displaystyle \dfrac { \Delta h }{ h } =\dfrac { \alpha }{ 100 } $
$\Rightarrow \displaystyle  { \Delta h }=\dfrac {\alpha h }{ 100 } $
Now, approximate error in measuring V$\displaystyle =dV= (\dfrac{dV}{dh}){ \Delta h}$
                                          $\displaystyle = \dfrac{3\alpha }{100} {\pi h^{3}} =3\alpha$% of V
Percentage error in measuring $V =3\alpha$%

The pressure P and volume V of a gas are connected by the relation $PV^{1/4}=constant$. The percentage increase in the pressure corresponding to a deminition of $\dfrac12 \%$ in the volume is

  1. $\dfrac {1}{2}$ %

  2. $\dfrac {1}{4}$ %

  3. $\dfrac {1}{8}$ %

  4. none of these


Correct Option: C
Explanation:
$PV^{1/4}=constant$
$\displaystyle \Rightarrow P=\dfrac{k}{V^{{1}/{4}}}$
$\displaystyle \Rightarrow \dfrac{dP}{dV}=-\dfrac{k}{4}V^{-{5}/{4}}$
Percentage error in V $\displaystyle= -\dfrac{1}{2}\%$
$\Rightarrow\displaystyle \dfrac{\Delta V}{V} =-\dfrac{1}{200}$
$\Rightarrow\displaystyle {\Delta V}=-\dfrac{V}{200}$
Approximate change in $P\displaystyle=dP=(\dfrac{dP}{dV}){\Delta V}$
                                           $\displaystyle  =\dfrac{1}{800} {kV^{-1/4}}=\dfrac{1}{8}\%$ of P
Percentage increase in  $V \ \displaystyle =\dfrac{1}{8}\%$

If the ratio of base radius and height of a cone is 1:2 and percentage error in radius is $\lambda$ %, then the error in its volume is

  1. $\lambda$ %

  2. $2\lambda$%

  3. $3\lambda$%

  4. none of these


Correct Option: A
Explanation:
Volume of cone $V=\dfrac { 1 }{ 3 } \pi { r }^{ 2 }h $
Given, $\displaystyle \dfrac{r}{h}=\dfrac{1}{2}$
$\Rightarrow V=\dfrac { 2 }{ 3 } \pi { r }^{ 3 } $
$\displaystyle \dfrac{dV}{dr}=2\pi r^{2}$
Percentage error in measuring r $=\lambda$%
$\Rightarrow \displaystyle \dfrac{\Delta r}{r}=\dfrac{\lambda}{100}$
$\Rightarrow \displaystyle \Delta r =\dfrac{\lambda r}{100}$
Approximate error in V $\displaystyle=dV=(\dfrac{dV}{dr}) \Delta r $
                                      $\displaystyle=\dfrac{\lambda}{100} (2\pi r^{3})=\lambda\%$ of V
Percentage error in $V =\lambda\%$

If $y=x^n$, then the ratio of relative errors in $y$ and $x$ is

  1. $1:1$

  2. $2:1$

  3. $1:n$

  4. $n:1$


Correct Option: D
Explanation:
$y=x^{n}$
$\Rightarrow \displaystyle \dfrac{dy}{dx}=nx^{n-1}$
Approximate error in y is $\displaystyle dy=\left (\dfrac{dy}{dx}\right) \Delta x$
                                      $=nx^{n-1} \Delta x$
Relative error in y is $\displaystyle \dfrac{dy}{y}=\dfrac{n}{x}\Delta x$
Approximate error in x is $\displaystyle dx=\left (\dfrac{dx}{dy}\right) \Delta y$
                                     $\displaystyle=\dfrac{1}{nx^{n-1}} \Delta y$
Relative error in x is $\displaystyle \dfrac{dx}{x}=\dfrac{1}{nx^{n}}\Delta y$
Required ratio $\displaystyle = \dfrac{\dfrac{n}{x}\Delta x}{\dfrac{1}{nx^{n}}\Delta y}$
                               $\displaystyle =n^{2}x^{n-1} \dfrac{\Delta x}{\Delta y}$
                               $\displaystyle =\dfrac{n}{1}$
So, the ratio of relative errors in y and x is $ n:1$.

The circumference of a circle is measured as $28 cm$ with an error of $0.01 cm$. The percentage error in the area is

  1. $\dfrac {1}{14}$

  2. $0.01$

  3. $\dfrac {1}{7}$

  4. none of these


Correct Option: A
Explanation:

Circumference $C=2\pi r$
$\Rightarrow\displaystyle r=\frac{14}{\pi}$
Also, $\displaystyle \frac{dC}{dr}=2\pi$
Area of circle $A=\pi r^{2} $
$\Rightarrow\displaystyle A=\frac{{14}^{2}}{\pi}$
Also, $\displaystyle \frac{dA}{dr}=2\pi r$
$\displaystyle \Rightarrow \frac{dA}{dC}=r=\frac{14}{pi}$
Approximate error in $A$ is $\displaystyle dA=( \frac{dA}{dC}) \Delta C$
                           $\displaystyle=\frac{14}{\pi}\frac{1}{100}$
                            $\displaystyle=\frac{1}{1400}$ of A
Percentage error in $A \ \displaystyle =\frac{1}{14}\%$

If there is an error of $0.01 cm$ in the diameter of a sphere then percentage error in surface area when the radius $= 5 cm$, is

  1. $0.005\%$

  2. $0.05\%$

  3. $0.1\%$

  4. $0.2\%$


Correct Option: D
Explanation:

Surface area of sphere $S=4\pi r^{2}$
$\displaystyle S=\pi D^{2}$
$\Rightarrow S=100\pi$
Also, $ \displaystyle \frac{dS}{dD}=2\pi D=20\pi$
Approximate error in S is $\displaystyle dS=(\frac{dS}{dD})\Delta D$
                                         $ =20\pi (0.01)$
                                          $=\dfrac{1}{500} S$
                                           $=0.2$% of S
Percentage error in $S=0.2%$

If the percentage error in the edge of a cube is 1, then error in its volume is

  1. $1 \%$

  2. $2 \%$

  3. $3 \%$

  4. none of these


Correct Option: C
Explanation:
Volume of cube $V=x^{3}$
$\Rightarrow \displaystyle \dfrac{dV}{dx}=3x^{2}$
Percentage error in x is 1%.
$\Rightarrow \displaystyle \dfrac{\Delta x}{x}=\dfrac{1}{100}$
$\Rightarrow \displaystyle \Delta x=\dfrac{x}{100}$
Approximate error in V $\displaystyle=dV=(\dfrac{dV}{dx}) \Delta x$
                                  $\displaystyle = \dfrac{3{x}^{3}}{100}$                              
Percentage error in V $\displaystyle= \dfrac{dV}{V} $
                                   $\displaystyle=\dfrac{3}{100}=3\%$

In a $\Delta ABC$ if sides a and b remain constant such that $\alpha$ is the error in C, then relative error in its area is

  1. $\alpha \cot C$

  2. $\alpha \sin C$

  3. $\alpha\tan C$

  4. $\alpha\cos C$


Correct Option: A
Explanation:
Area of triangle $S\displaystyle =\dfrac {1}{2}ab \sin C$
$\displaystyle \Rightarrow \dfrac {dS}{dC}=\dfrac {1}{2}ab \cos C$
Now, approximate error in S is $\Delta S=\dfrac {dS}{dC}\Delta C$
$\displaystyle\Rightarrow \Delta S=\dfrac {1}{2}ab \cos C \alpha              [\because \Delta C=\alpha]$
$\displaystyle\Rightarrow \dfrac {\Delta S}{S}=\dfrac {\dfrac {1}{2}ab \cos C}{\dfrac {1}{2}ab \sin C}\alpha=\alpha \cot C$

In a $\Delta ABC$ the sides b and c are given. If there is an error $\Delta A$ in measuring angle A, then the error $\Delta a$ in side a is given by

  1. $\dfrac {S}{2a}\Delta A$

  2. $\dfrac {2S}{a}\Delta A$

  3. bc sin A $\Delta A$

  4. none of these


Correct Option: B
Explanation:

In $\triangle ABC$ we have
$\Rightarrow d\left( 2bc\cos { A }  \right) =d\left( { b }^{ 2 }+{ c }^{ 2 }-{ a }^{ 2 } \right) \ \Rightarrow -2bc\sin { A } dA=-2ada\ \Rightarrow bc\sin { A } dA=ada$
$\displaystyle \Rightarrow \frac { 2 }{ a } \left( \frac { 1 }{ 2 } bc\sin { B }  \right) dA=da$
$\displaystyle \Rightarrow da=\frac { 2S }{ a } dA$
$\displaystyle \Rightarrow \triangle a=\frac { 2S }{ a } dA\ \left[ \because dx\equiv \triangle a\quad and\quad dA=BA \right] $

If errors of $1\%$ each are made in the base radius and height of a cylinder, then the percentage error in its volume is

  1. $1\%$

  2. $2\%$

  3. $3\%$

  4. none of these


Correct Option: C
Explanation:

Given, percentage error in r is 1%
$\Rightarrow \displaystyle \frac{\Delta r}{r}=\frac{1}{100}$

$\Rightarrow \displaystyle \Delta r=\frac{r}{100}$
Also given, percentage error in h is 1%
$\Rightarrow \displaystyle \frac{\Delta h}{h}=\frac{1}{100}$

$\Rightarrow \displaystyle \Delta h=\frac{h}{100}$
Now, volume of cylinder $V=\pi r^{2}h$
$\Delta V=\pi [r^{2}\Delta h+2rh\Delta r]$
$\displaystyle \Delta V=\pi[r^{2}\frac{h}{100}+2rh\frac{r}{100}]$

$\displaystyle\Delta V=\pi r^{2}h[\frac{3}{100}]$
$\Rightarrow\displaystyle\frac{\Delta V}{V}=\frac{3}{100}$
Percentage error in V is 3%
 

The circumference of a circle is measured as $56$ cm with an error $0.02$ cm. The percentage error in its area is

  1. $\dfrac {1}{7}$

  2. $\dfrac {1}{28}$

  3. $\dfrac {1}{14}$

  4. $\dfrac {1}{56}$


Correct Option: C
Explanation:

Circumference of circle $C=2\pi r=56cm$


$\Rightarrow \displaystyle r=\frac{28}{\pi}$

Also, $\displaystyle \frac{dC}{dr}=2\pi$

Area of circle $A=\pi r^{2}$

$\displaystyle \frac{dA}{dr}=2\pi r$

$\Rightarrow\displaystyle \frac{dA}{dC}=r =\frac{28}{\pi}$

Approximate error in A $=\displaystyle dA=(\frac{dA}{dC})\Delta C$

                                      $= r (0.02)$

$\Rightarrow\displaystyle \frac{dA}{A}= \frac{0.02}{\pi r}=\frac{1}{1400}$

Percentage error in A is $\displaystyle\frac{1}{14}$%

If an error of $1^o$ is made in measuring the angle of a sector of radius $30 \ cm$, then the approximate error in its area is

  1. $450 cm^2$

  2. $25\pi cm^2$

  3. $2.5\pi cm^2$

  4. none of these


Correct Option: C
Explanation:
Area of sector $\displaystyle A=\dfrac{\pi r^{2}\theta}{360}$
Given $r=30 cm, d{\theta}=1^{0}$
Approximate error in A is $\displaystyle=dA=(\dfrac{dA}{d\theta})\Delta \theta$
                             $\displaystyle = \dfrac{900\pi}{360} $
$\displaystyle \Rightarrow dA =2.5 \pi cm^{2}$

If error in  measuring the edge of a cube is $k$% then the percentage error in estimating its volume is

  1. $k$

  2. $3k$

  3. $\displaystyle \frac{k}{3}$

  4. none of these


Correct Option: B
Explanation:

Let the actual length of the cube be a.

Therefore the measured length of the cube will be 
$=a(1\pm0.0k)$
$=a(1\pm\dfrac{k}{100})$
Considering positive error, 
$a'=a(1+\dfrac{k}{100})$
$V'=a^{3}(1+\dfrac{k}{100})^{3}$

$=a^{3}(1+3(\dfrac{k}{100})+3(\dfrac{k}{100})^{2}+(\dfrac{k}{100})^{3})$

Since $\dfrac{k}{100}<<1$, hence we neglect the higher order terms.
Thus 
$V'=a^{3}(1+3(\dfrac{k}{100}))$

Actual volume V
$V=a^{3}$
Therefore 
$V'-V=a^{3}(1+\dfrac{3k}{100})-a^{3}$

$=a^{3}(\dfrac{3k}{100})$

$\dfrac{V'-V}{V}=\dfrac{a^{3}\dfrac{3k}{100}}{a^{3}}$

$=\dfrac{3k}{100}$

$=\dfrac{3k}{100}$

$\dfrac{V'-V}{V}\times 100=3k$
Therefore percentage error in volume is $3k$.

If the radius of a sphere is measured as $9 \ cm$ with an error of $ 0.03 \ cm$ then, find the approximate error in calculating its volume.

  1. $\displaystyle 9.72\pi:: cm^{3}$

  2. $\displaystyle 7.92\pi:: cm^{3}$

  3. $\displaystyle 8.72\pi:: cm^{3}$

  4. None of these


Correct Option: A
Explanation:

Given, $r=9 cm, \Delta r=0.03cm$

We know Volume of sphere with radius 'r' is $V=\cfrac{4}{3}\pi r^3$
$\therefore \Delta V=4\pi r^2\Delta r$
$\Rightarrow \Delta V=4\pi\times 81\times .03=9.72\pi  cm^3 $(using given values)

The percentage error in the $11^{th}$ root of the number $28$ is approximately ____________ times the percentage error in $28$

  1. $\dfrac { 1 }{ 28 } $

  2. $\dfrac { 1 }{ 11 } $

  3. $11$

  4. $28$


Correct Option: B
Explanation:

Suppose $y = x^{11}$

$dy = 11x^{10}dx$
Dividing by y on both sides, we have $ \cfrac{\Delta y}{y} = \cfrac{11x^{10}\Delta x}{y} = \cfrac{11x^{10}\Delta x}{x^{11}}$
$\therefore \cfrac{\Delta y}{y} = \cfrac{11 \Delta x}{x}$

Here, when $y = 28$, $x$ will be the $11^{th}$ root of $28$.
$\therefore \cfrac{\Delta (28)}{28} = \cfrac{11 \Delta (\sqrt[11]{28})}{\sqrt[11]{28}}$
Hence, the percentage error in the $11$th root of $28$ would approximately be $\cfrac{1}{11}$ times the error in $28$

State true or false:
By the method of Newton-Raphson, the cube root of $10$ after the first iteration is $2.167$.

  1. True

  2. False


Correct Option: A
Explanation:
Let $f\left( x \right) ={ x }^{ 3 }-10$
$f\left( x \right) =3{ x }^{ 2 }$
Letting initial guess be ${ x } _{ 0 }=2$ (${ 2 }^{ 3 }=8$ which is close to $10$)
We have
${ x } _{ 1 }=2-\left[ \cfrac { { (2) }^{ 3 }-10 }{ 3\times { (2) }^{ 2 } }  \right] \quad \left[ \because { x } _{ n+1 }={ x } _{ n }-\cfrac { f\left( { x } _{ n } \right)  }{ f'\left( { x } _{ n } \right)  }  \right] $
${ x } _{ 1 }=2-\left[ \cfrac { -2 }{ 12 }  \right] $
${ x } _{ 1 }=2+\cfrac { 1 }{ 6 } $
${ x } _{ 1 }=2+0.167$
${ x } _{ 1 }=2.167$

By Newton - Raphson's method the formula for finding the square root of any number $y$ is:

  1. $x _{n + 1} = \dfrac {1}{2}\left [x _{n} + \dfrac {y}{x _{n}}\right ]$

  2. $x _{n + 1} = \dfrac {1}{2}\left [x _{0} + \dfrac {y}{x _{0}}\right ]$

  3. $x _{n + 1} = \dfrac {1}{3}\left [2x _{n} + \dfrac {y}{x _{n}^{2}}\right ]$

  4. $x _{n + 1} = \dfrac {1}{3}\left [2x _{0} + \dfrac {y}{x _{0}^{2}}\right ]$


Correct Option: A
Explanation:
Let $x = \sqrt { y } $
$\implies { x }^{ 2 } = y$
$\implies { x }^{ 2 }-y = 0$
Iterative eqn. for Newton Raphson method is

${ x } _{ n+1 } = { { x } _{ n } }-\dfrac { f({ { x } _{ n } }) }{ f\prime ({ { x } _{ n } }) } $ 

Substitute $f(x) = { x }^{ 2 }-y$
$\implies f'(x) = 2x$ ........... $[\because\ y$ is any number $\therefore  f'(y) =0]$

     ${ x } _{ n+1 } = { { x } _{ n } }-\dfrac { { x } _{ n }^{ 2 }-y }{ 2{ x } _{ n } } $ 
              $= { x } _{ n }-\dfrac { { x } _{ n }^{ 2 } }{ 2{ x } _{ n } } +\dfrac { y }{ 2{ x } _{ n } } $ 

               $= { x } _{ n }-\dfrac { { x } _{ n } }{ 2 } +\dfrac { y }{ 2{ x } _{ n } } $
 
    ${ x } _{ n+1 } = \dfrac { { x } _{ n } }{ 2 } +\dfrac { y }{ 2{ x } _{ n } } $ 

    $\boxed { { x } _{ n+1 } = \dfrac { 1 }{ 2 } \left[ { x } _{ n }+\dfrac { y }{ { x } _{ n } }  \right]  } $ 

The value of $\cdot4125\ E\ 05 \times \cdot3781\ E01.$ is?

  1. $\cdot8203825\ E\ 09$

  2. $\cdot8303645\ E\ 06$

  3. $\cdot1559662\ E\ 06$

  4. $\cdot8305645\ E\ 09$


Correct Option: C
Explanation:

$0.4125:E:05 \times 0.3781:E:01=?$

The Scientific format displays a number in exponential notation, replacing part of the number with $E+n$, where $E$ (stands for exponent) multiplies the preceding number by $10$ to the $n^{th}$ power.

That is $1.23E+10$ can be written as $1.23 \times 10^{10}$

$0.4125:E:05 \times 0.3781:E:01=(0.4125 \cdot 10^5) \times (0.3781 \cdot 10^1)$

                                                 $=(0.4125 \times 0.3781)10^6$

                                                 $=0.1559662 \times 10^6$

$0.4125:E:05 \times 0.3781:E:01=0.1559662:E:06$

The value of $\cdot7378\ E\ 05 -\cdot2347\ E05.$ is?

  1. $\cdot12057\ E\ 09$

  2. $\cdot12057\ E\ 05$

  3. $\cdot64045\ E\ 09$

  4. $\cdot5031\ E\ 05$


Correct Option: D
Explanation:

We need to find value of $\cdot7378\ E\ 05 -\cdot2347\ E05.$
Take out $E05$ common to get 
$ (.7378-.2347)E05$ $= \cdot5031\ E\ 05 $

The value of $\cdot4365\ E\ 05 +\cdot2735\ E06$ is?

  1. $\cdot12057\ E\ 09$

  2. $\cdot31715\ E\ 06$

  3. $\cdot64045\ E\ 09$

  4. $\cdot517336\ E\ 09$


Correct Option: B
Explanation:

$⋅4365 E 05+⋅2735 E06 = (.04365+.2735)E06$4

$=(.31715)E06$

The value of $\cdot4657\ E\ - 12 -\cdot4624$ is?

  1. $\cdot12057\ E\ 09$

  2. $\cdot0033\ E-12$

  3. $\cdot0033\ E\ 09$

  4. $\cdot12057\ E\ 05$


Correct Option: B
Explanation:

$0.4657E-12-0.4624E=(0.4657E-0.4624E)-12$
                                              $=0.0033E-12$
Therefore the value of $0.4657E-12-0.4624E$ is $0.0033E-12$


The value of $\cdot3214\ E\ - 02 \times \cdot3781\ E\ 05.$ is?

  1. $\cdot699045\ E\ 05$

  2. $\cdot699045\ E\ 02$

  3. $\cdot699055\ E\ 02$

  4. $\cdot698045\ E\ 02$


Correct Option: B

The percentage error in the surface area of a cube with edge x cm, when the edge is increased by $11\%$ is _________.

  1. $11$

  2. $22$

  3. $10$

  4. $44$


Correct Option: B
Explanation:

Surface area of cube $=$ S $=6x^2$
$\therefore \dfrac{dS}{dt}=12x\dfrac{dx}{dt}$
Side of cube increase $11\%$.
$\therefore \dfrac{dx}{dt}=11\%$ increment in side
$=\dfrac{11x}{100}$
$\therefore \dfrac{dx}{dt}=12\left(\dfrac{11x}{100}\right)$
$=6\left(\dfrac{22}{100}\right)x^2$
$=6x^2\left(\dfrac{22}{100}\right)$
$=22\%$ in surface area
$\therefore$ Surface area increase $22\%$.

The focal length of a mirror is given by $\dfrac {1}{v}-\dfrac {1}{u}=\dfrac {2}{f}$. If equal errors ($\alpha$) are made in measuring $u$ and $v$, then the relative error in $f$ is

  1. $\dfrac {2}{\alpha}$

  2. $\alpha \left (\dfrac {1}{u}+\dfrac {1}{v}\right )$

  3. $\alpha \left (\dfrac {1}{u}-\dfrac {1}{v}\right )$

  4. none of these


Correct Option: B
Explanation:

Given, $\displaystyle \dfrac {1}{v}-\dfrac {1}{u}=\dfrac {2}{f}$
$\Rightarrow \displaystyle -\dfrac {\Delta v}{v^2}+\dfrac {\Delta u}{u^2}=-\dfrac {2\Delta f}{f^2}$
Since, given equal errors in measuring u and v i.e.$\Delta u=\Delta v=\alpha$
$\Rightarrow {\alpha}\left(\dfrac{1}{u}-\dfrac{1}{v}\right)\left(\dfrac{1}{u}+\dfrac{1}{v}\right)=-\dfrac {2\Delta f}{f^2}$
But, $\dfrac{1}{v}-\dfrac{1}{u}=\dfrac{2}{f}$
$\Rightarrow\displaystyle \frac{ \Delta f}{f}={\alpha}\left(\dfrac{1}{u}+\dfrac{1}{v}\right)$
Hence, correct option is B

The period of oscillation $T$ of a pendulum of length $l$ at a place of acceleration due to gravity $g$ is given by $T=2\pi \sqrt {\dfrac {l}{g}}$. If the calculated length is $0.992$ times the actual length and if the value assumed for $g$ is $1.002$ times its actual value, the relative error in the computed value of $T$ is

  1. $0.005$

  2. $-0.005$

  3. $0.003$

  4. $-0.003$


Correct Option: B
Explanation:

Relative error will calculate by
$\dfrac{\Delta T}{T}=\dfrac{1}{2}\left[\dfrac{\Delta L}{L}-\dfrac{\Delta g}{g}\right]$

$\dfrac{\Delta T}{T}=\dfrac{1}{2}\left[\dfrac{0.992L}{L}-\dfrac{1.002 g}{g}\right]$

$\Delta T=-0.005T$

The area of a triangle is computed using the formula $S=\dfrac {1}{2}$ bc sin A. If the relative errors made in measuring b, c and calculating S are respectively $0.02$, $0.01$ and $0.13$ the approximate error in A when $A=\pi /6$ is

  1. $0.05$ radians

  2. $0.01$ radians

  3. $0.05$ degree

  4. $0.01$ degree


Correct Option: A
Explanation:

Error formula for given equation is
$\dfrac{\Delta s}{s}=\dfrac{\Delta b}{b}+\dfrac{\Delta c}{c}+\dfrac{\Delta sinx}{sinx}$
$0.13=0.02+0.01+\dfrac{\Delta sinx}{1/2}$
$\Delta sinx=0.05$

Using Newton-Raphson method, the cube root of $24$ is?

  1. $2.884$

  2. $3.256$

  3. $5.231$

  4. $4.526$


Correct Option: A
Explanation:

To find the cube root of $24$ using Newton - Raphson method,
we need to solve $f(x)=x^3-24$.

$ \Rightarrow f'(x)=3x^2$

Notice $3^3=27$

Therefore the cube root of $24$ is slightly less than $3$.

We have $f(x)=x^3-24, f'(x)=3x^2$

Let us start estimating the root $x$

Let the first estimation be $a=2.9$ (slightly less than 3)

Hence the subsequent estimates will be $b=a-\dfrac{f(a)}{f'(a)},c=b-\dfrac{f(b)}{f'(b)}$.

$f(a)=f(2.9)=(2.9)^3-24=0.389$ and $f'(a)=f'(2.9)=3(2.9)^2=25.23$

Therefore $b=2.9-\dfrac{0.389}{25.23}\approx 2.88458$

Now $c=2.88458-\dfrac{f(2.88458)}{f'(2.88458)}=2.88449$

Hence the cube root of $24$ is $2.884$

Using successive Bisection method find the second, third and fourth approximation of root of the  equation $x^3-3x-5=0$ in the interval $(2,2.5)$

  1. $ 2.375,2.135 \  &amp; \ \ 2.2815$

  2. $1.25,1.375 \ \ &amp; \ \ 1.4375$

  3. $4.23,3.214 \ \  &amp; \ \  2.135$

  4. $2.4475,2.175 \ \ &amp; \ \ 3.2815$


Correct Option: A
Explanation:

We have to find the second,third and fourth approximation of root of the equation $x^3-3x-5=0$ in the interval $(2,2.5)$ using successive Bisection method.

$\textbf{Iteration 1: k=0}$

$c _0=\dfrac{a _0+b _0}{2}=\dfrac{2+2.5}{2}=2.25$

Since $f(c _0)f(a _0)=f(2.25)f(2)>0$

Therefore set $a _1=2.25,b _1=b _0$

$\textbf{Iteration 2: k=1}$

$c _1=\dfrac{a _1+b _1}{2}=\dfrac{2.25+2.5}{2}=2.375$

Since $f(c _1)f(a _1)=f(2.375)f(2.25)<0$

Therefore set $a _2=a _1,b _2=c _1$

$\textbf{Iteration 3: k=2}$

$c _2=\dfrac{a _2+b _2}{2}=\dfrac{2.25+2.375}{2}=2.3125$

Since $f(c _2)f(a _2)=f(2.3125)f(2.25)<0$

Therefore set $a _3=a _2,b _3=c _2$

$\textbf{Iteration 4: k=3}$

$c _3=\dfrac{a _3+b _3}{2}=\dfrac{2.25+2.3125}{2}=2.28125$

Thus the second,third and fourth approximations are $2.375,2.3125,2.28125$ respectively.

The second and third approximation of $x^3-2x-5=0$ in the interval $(2,3)$ is?

  1. $x _2 = 2.0946$ and $x _3 = 2.0947$
  2. $x _2 = 1.636 $ and $x _3 = 2.98$
  3. $x _2 = 4.0946 $ and $x _3 = 5.0947$
  4. $x _2 = 2.946$ and $x _3 = 2.07$

Correct Option: A
Explanation:

Here, $x^3-2x-5=0$

Let $f(x)=x^3-2x-5$
$f'(x)=3x^2-2$
Here $f(2)=-1<0$ and $f(3)=16>0$
Root lies between $2$ and $3$.
$x _0=\dfrac{2+3}{2}=2.5$
First Iteration:
$f(x _0)=f(2.5)=5.625$
$f'(x _0)=f'(2.5)=16.75$
$x _1=x _0-\dfrac{f(x _0)}{f'(x _0)}=2.5-\dfrac{5.625}{16.75}=2.16418$
Second Iteration:

$f(x _1)=f(2.16418)=0.80795$
$f'(x _1)=f'(2.16418)=12.05101$
$x _2=x _1-\dfrac{f(x _1)}{f'(x _1)}=2.16418-\dfrac{0.80795}{12.05101}=2.09714$

Third Iteration:

$f(x _2)=f(2.09714)=0.02888$
$f'(x _2)=f'(2.09714)=11.19393$
$x _3=x _2-\dfrac{f(x _2)}{f'(x _2)}=2.09714-\dfrac{0.02888}{11.19393}=2.09456$

The second and third approximation to the roots of $x^4-x-10=0$ in the interval $(1,2)$ is?

  1. $x _2=2.856,x _3=3.8561$

  2. $x _2=1.7756,x _3=1.061$

  3. $x _2=1.87409, x _3=1.85587$
  4. $x _2=7.856,x _3=1.8561$


Correct Option: C
Explanation:

Here, $x^4-x-10=0$


Let $f(x)=x^4-x-10$

$f'(x)=4x^3-1$

Here $f(1)=-10<0$ and $f(2)=4>0$

Root lies between $1$ and $2$

$x _0=\dfrac{1+2}{2}=1.5$

First Iteration:

$f(x _0)=f(1.5)=-6.4375$

$f'(x _0)=f'(1.5)=12.5$

$x _1=x _0-\dfrac{f(x _0)}{f'(x _0)}=1.5-\dfrac{-6.4375}{12.5}=2.015$

Second Iteration:


$f(x _1)=f(2.015)=4.47043$

$f'(x _1)=f'(2.015)=31.72541$

$x _2=x _1-\dfrac{f(x _1)}{f'(x _1)}=2.015-\dfrac{4.47043}{31.72541}=1.87409$


Third Iteration:


$f(x _2)=f(1.87409)=0.46155$

$f'(x _2)=f'(1.87409)=25.32882$

$x _3=x _2-\dfrac{f(x _2)}{f'(x _2)}=1.87409-\dfrac{0.46155}{25.32882}=1.85587$

Using successive Bisection method find the second, third and fourth approximation of root of the given  equation $x^3-x-4=0$ in the interval $(1,2)$

  1. $2.75,13.875 , 1.8125$

  2. $1.75,1.875 , 1.8125$

  3. $1.725,1.5 , 1.8125$

  4. $2.75,1.875 , 1.8125$


Correct Option: B
Explanation:

We have to find the second,third and fourth approximation of root of the equation $x^3-x-4=0$ in the interval $(1,2)$ using successive Bisection method.

$\textbf{Iteration 1: k=0}$

$c _0=\dfrac{a _0+b _0}{2}=\dfrac{1+2}{2}=1.5$

Since $f(c _0)f(a _0)=f(1.5)f(1)>0$

Therefore set $a _1=1.5,b _1=b _0$

$\textbf{Iteration 2: k=1}$

$c _1=\dfrac{a _1+b _1}{2}=\dfrac{1.5+2}{2}=1.75$

Since $f(c _1)f(a _1)=f(1.75)f(1.5)>0$

Therefore set $a _2=c _1,b _2=b _1$

$\textbf{Iteration 3: k=2}$

$c _2=\dfrac{a _2+b _2}{2}=\dfrac{1.75+2}{2}=1.875$

Since $f(c _2)f(a _2)=f(1.875)f(1.75)<0$

Therefore set $a _3=a _2,b _3=c _2$

$\textbf{Iteration 4: k=3}$

$c _3=\dfrac{a _3+b _3}{2}=\dfrac{1.75+1.875}{2}=1.8125$

Thus the second,third and fourth approximations are $1.75,1.875,1.8125$ respectively.

The second approximation of roots of $x^3-x-4=0$ in the interval $(1,2)$ by the method of false position is?

  1. $1.78049$

  2. $1.276$

  3. $2.123$

  4. $0.726$


Correct Option: A
Explanation:

Here, $f(x)=x^3-x-4=0$


first iteration:

]Here $f(1)=-4<0$ and $f(2)=2>0$

Now, root lies between $x _0=1$ and $x _1=2$

$x _2=x _0-f(x _0) \times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=1-(-4)\times \dfrac{2-1}{2-(-4)}=1.66667$

$f(x _2)=f(1.66667)=-1.03704<0$

2nd iteration:

Here $f(1.66667)=-1.03704<0$ and $f(2)=2>0$

Now, root lies between $x _0=1.66667$ and $x _1=2$

$x _3=x _0-f(x _0) \times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=1.67-(-1.04)\times \dfrac{2-1.67}{2-(-1.04)}=1.78049$

Using successive Bisection method find the second, third and fourth approximation of root of the equation $x^3+x^2-1$ in the interval $(0,1)$

  1. $0.75,1.875,0.8125$

  2. $1.75,0.875,0.8125$

  3. $0.75,0.875,0.8125$

  4. $0.75,0.875,1.8125$


Correct Option: C
Explanation:

We have to find the second,third and fourth approximation of root of the equation $x^3+x^2-1=0$ in the interval $(0,1)$ using successive Bisection method.

$\textbf{Iteration 1: k=0}$

$c _0=\dfrac{a _0+b _0}{2}=\dfrac{0+1}{2}=0.5$

Since $f(c _0)f(a _0)=f(0.5)f(0)>0$

Therefore set $a _1=0.5,b _1=b _0$

$\textbf{Iteration 2: k=1}$

$c _1=\dfrac{a _1+b _1}{2}=\dfrac{0.5+1}{2}=0.75$

Since $f(c _1)f(a _1)=f(0.75)f(0.5)>0$

Therefore set $a _2=c _1,b _2=b _1$

$\textbf{Iteration 3: k=2}$

$c _2=\dfrac{a _2+b _2}{2}=\dfrac{0.75+1}{2}=0.875$

Since $f(c _2)f(a _2)=f(0.875)f(0.75)<0$

Therefore set $a _3=a _2,b _3=c _2$

$\textbf{Iteration 4: k=3}$

$c _3=\dfrac{a _3+b _3}{2}=\dfrac{0.75+0.875}{2}=0.8125$

Thus the second,third and fourth approximations are $0.75,0.875,0.8125$ respectively.

The third approximation of roots of $x^3-x^2-1=0$ in the interval $(1,2)$ by the method of false position is?

  1. $2.430$

  2. $1.340$

  3. $1.430$

  4. $1.230$


Correct Option: C
Explanation:

Here, $x^3-x^2-1=0$

Let $f(x)=x^3-x^2-1$
First Iteration:
Here, $f(1)=-1<0$ and $f(2)=3>0$
Now, Root lies between $x _0=1$ and $x _1=2$
$x _2=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=1-(-1)\times \dfrac{2-1}{3-(-1)}=$
Second Iteration:
Here, $f(1.25)=-0.60938<0$ and $f(2)=3>0$

Now, Root lies between $x _0=1.25$ and $x _1=2$
$x _3=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=1.25-(-0.61)\times \dfrac{2-1.25}{3-(-0.61)}=1.37662$

Third Iteration:

Here, $f(1.37662)=-0.28626<0$ and $f(2)=3>0$
Now, Root lies between $x _0=1.37662$ and $x _1=2$
$x _4=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=1.38-(-0.29)\times \dfrac{2-1.38}{3-(-0.29)}=1.43093$

The third approximation of roots of $x^3-x-1=0$ in the interval $(1,2)$ by the method of false position is?

  1. $1.011$

  2. $2.265$

  3. $1.255$

  4. $1.294$


Correct Option: D
Explanation:

Here, $x^3-x-1=0$

Let $f(x)=x^3-x-1$
First Iteration:
Here, $f(1)=-1<0$ and $f(2)=5>0$
Now, Root lies between $x _0=1$ and $x _1=2$
$x _2=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=1-(-1)\times \dfrac{2-1}{5-(-1)}=1.16667$
Second Iteration:
Here, $f(1.16667)=-0.5787$ and $f(2)=5>0$

Now, Root lies between $x _0=1.16667$ and $x _1=2$
$x _3=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=1.17-(-0.58)\times \dfrac{2-1.17}{5-(-0.58)}=1.25311$

Third Iteration:

Here, $f(1.25311)=-0.28536$ and $f(2)=5>0$
Now, Root lies between $x _0=1.25311$ and $x _1=2$
$x _4=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=1.25-(-0.29)\times \dfrac{2-1.25}{5-(-0.29)}=1.29344$

The value of $\cdot8642\ E\ 02 \div \cdot2562\ E02.$ is?

  1. $\cdot12057\ E\ 09$

  2. $\cdot33715\ E\ 01$

  3. $\cdot33715\ E\ 05$

  4. $\cdot33725\ E\ 01$


Correct Option: B
Explanation:

$0.8642:E:02 \div 0.2562 : E: 02 = ?$

The Scientific format displays a number in exponential notation, replacing part of the number with $E+n$, where $E$ (stands for exponent) multiplies the preceding number by $10$ to the $n^{th}$ power.

That is $1.23E+10$ can be written as $1.23 \times 10^{10}$

$0.8642:E:02 \div 0.2562 : E: 02 = \dfrac{0.8642 \times 10^2}{0.2562 \times 10^2} $

                                                 $=\dfrac{0.8642}{0.2562}$

                                                $=3.371459$

                                                $=0.3371459 \times 10^1$

                                                $=0.33715 : E : 01$

$0.8642:E:02 \div 0.2562 : E: 02 =0.33715 : E : 01$

The second approximation of roots of $x^3-5x-7=0$ in the interval $(2,3)$ by the method of false position is?

  1. $1.735$

  2. $2.375$

  3. $3.735$

  4. $2.735$


Correct Option: D
Explanation:

Here, $x^3-5x-7=0$

Let $f(x)=x^3-5x-7$
First Iteration:
Here, $f(2)=-9<0$ and $f(3)=5>0$
Now, Root lies between $x _0=2$ and $x _1=3$
$x _2=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=2-(-9)\times \dfrac{3-2}{5-(-9)}=2.64286$
Second Iteration:
Here, $f(2.64286)=-1.75474$ and $f(3)=5>0$

Now, Root lies between $x _0=2.64286$ and $x _1=3$
$x _3=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=2.64-(-1.75)\times \dfrac{3-2.64}{5-(-1.75)}=2.73564$

The third approximation of root of $x^3-x^2-1=0$ in the interval $(1,2)$ using successive bisection method is?

  1. $1.475$

  2. $1.375$

  3. $2.213$

  4. $1.564$


Correct Option: B
Explanation:

We have to find the third approximation of root of the equation $x^3-x^2-1=0$ in the interval $(1,2)$ using successive Bisection method.

$\textbf{Iteration 1: k=0}$

$c _0=\dfrac{a _0+b _0}{2}=\dfrac{1+2}{2}=1.5$

Since $f(c _0)f(a _0)=f(1.5)f(1)<0$

Therefore set $a _1=a _0,b _1=c _0$

$\textbf{Iteration 2: k=1}$

$c _1=\dfrac{a _1+b _1}{2}=\dfrac{1+1.5}{2}=1.25$

Since $f(c _1)f(a _1)=f(1.25)f(1)>0$

Therefore set $a _2=c _1,b _2=b _1$

$\textbf{Iteration 3: k=2}$

$c _2=\dfrac{a _2+b _2}{2}=\dfrac{1.25+1.5}{2}=1.375$

Thus the third approximation of the root is $1.375$ respectively.

By successive bisection method, the cube root of $2$ between the interval (1,1.5)_is?

  1. $1.2813$

  2. $1.2121$

  3. $1.013$

  4. $1.475$


Correct Option: A
Explanation:

Function can be written as $f(x)=x^3-2$


First Iteration:
$f(1)=-1<0$ and $f(1.5)=1.375>0$
Now, root lies between $1$ and $1.5$
So,
$x _0=\dfrac{1+1.5}{2}=1.25$
$f(x _0)=-0.04688<0$

Second Iteration:

$f(1.25)=-0.04688<0$ and $f(1.5)=1.375>0$
Now, root lies between $1.25$ and $1.5$
So,
$x _1=\dfrac{1.25+1.5}{2}=1.375$

$f(x _1)=0.59961>0$

Third Iteration:

$f(1.25)=-0.04688<0$ and $f(1.375)=0.59961>0$
Now, root lies between $1.25$ and $1.375$
So,
$x _2=\dfrac{1.25+1.375}{2}=1.3125$
$f(x _2)=0.26099>0$

Fourth Iteration:
$f(1.25)=-0.04688<0$ and $f(1.3125)=0.26099>0$
Now, root lies between $1.25$ and $1.3125$
So,
$x _2=\dfrac{1.25+1.3125}{2}=1.28125\approx 1.2813$

The value of $\cdot4267\ E\ 10 \div \cdot2437\ E -02.$ is?

  1. $\cdot1751\ E\ 03$

  2. $\cdot1752\ E\ 13$

  3. $\cdot1751\ E\ 13$

  4. $\cdot1762\ E\ 13$


Correct Option: C
Explanation:

$0.4267:E:10\div0.2437 : E :-02=?$

The Scientific format displays a number in exponential notation, replacing part of the number with $E+n$, where $E$ (stands for exponent) multiplies the preceding number by $10$ to the $n^{th}$ power.

That is $1.23E+10$ can be written as $1.23 \times 10^{10}$

$0.4267:E:10\div0.2437 : E :-02=\dfrac{0.4267 \times 10^{10}}{0.2437 \times 10^{-2}}$

                                                       $= 1.75092 \times 10^{12}$

                                                       $= 1.751 \times 10^{12}$

                                                       $= .1751 \times 10^{13}$

                                                       $= 0.1751 : E :13$

Hence $0.4267:E:10\div0.2437 : E :-02=0.1751 : E :13$

The third approximation of roots of $x^3-9x+1=0$ in the interval $(2,4)$ by the method of false position is?

  1. $8.23$

  2. $1.25$

  3. $2.85$

  4. $2.12$


Correct Option: C
Explanation:

Here, $x^3-9x+1=0$

Let $f(x)=x^3-9x+1$
First Iteration:
Here, $f(2)=-9<0$ and $f(4)=29>0$
Now, Root lies between $x _0=2$ and $x _1=4$
$x _2=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=2-(-9)\times \dfrac{4-2}{29-(-9)}=2.47368$
Second Iteration:
Here, $f(2.47368)=-6.1264$ and $f(2)=29>0$

Now, Root lies between $x _0=2.47368$ and $x _1=4$
$x _3=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=2.47-(-6.13)\times \dfrac{4-2.47}{29-(-6.13)}=2.73989$

Third Iteration:

Here, $f(2.73989)=-3.09067$ and $f(4)=29>0$
Now, Root lies between $x _0=2.73989$ and $x _1=4$
$x _4=x _0-f(x _0)\times \dfrac{x _1-x _0}{f(x _1)-f(x _0)}=2.74-(-3.09)\times \dfrac{4-2.74}{29-(-3.09)}=2.86125$

If the error committed in measuring the radius of the circle is $0.05\%$, then the corresponding error in calculating the area is:

  1. $0.05\%$

  2. $0.025\%$

  3. $0.25\%$

  4. $0.1\%$


Correct Option: D
Explanation:

$\dfrac { dr }{ r } =0.05\Rightarrow dr=(0.05)r$

Area of circle $=\pi r^2$
$\ A=\pi r^{ 2 }\Rightarrow \dfrac { dA }{ dr } =2\pi r\ dA=2\pi rdr\Rightarrow \dfrac { dA }{ A } =\dfrac { 2\pi rdr }{ \pi r^{ 2 } } =\dfrac { 2dr }{ r } \ \therefore \dfrac { dA }{ A } =2(0.05)^{ 2 }=0.1$
$\therefore$ Corresponding error in area $= 0.1\%$

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