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Reciprocal equations - class-X

Description: reciprocal equations
Number of Questions: 44
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Tags: theory of equations maths
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The equation $3x^4-5x^3+3x^2-4x+5=0$ is of the type

  1. Quadratic

  2. Linear

  3. Reiprocal

  4. None of the above


Correct Option: D
Explanation:

Given equation is $3x^4-5x^3+3x^2-4x+5=0$ .... $(i)$

The maximum power of $x$ in this equation is $ 4$, so this is $4th$ degree equation  
So, $(i)$ is neither linear nor quadratic equation.
In reciprocal equation ($ ax^4 +bx^3 +cx^2 +dx +e = 0 $)  the multiplication of the roots i.e ($\dfrac{e}{a}$) should be  $1$

In the given equation $(i)$, $\dfrac{e}{a}  = \dfrac{5}{3}$  
So the multiplication of roots is not equal to one
Therefore, equation $(i)$ is not a reciprocal equation.

Hence, option D is correct.

$x+\dfrac{1}{x}=2, x^{1680}+\dfrac{1}{x^{1680}}$

  1. $1$

  2. $-1$

  3. $2$

  4. $-2$


Correct Option: C
Explanation:

We have,

$x+\dfrac{1}{x}=2$
We know that if $x+\dfrac{1}{x}=2$, then
$x^n+\dfrac{1}{x^n}=2$
Therefore,
$x^{1680}+\dfrac{1}{x^{1680}}=2$

Simplify the reciprocal equation $\dfrac{3}{12}=\dfrac{3}{2x}$

  1. $0$

  2. $3$

  3. $6$

  4. $1$


Correct Option: C
Explanation:

Given equation is $\dfrac {3}{12}=\dfrac {3}{2x}$

$\Rightarrow 6x=36$
$\Rightarrow x=\dfrac {36}{6}$
$\Rightarrow x=6$
Therefore, the reciprocal of the given function is $6$.

Simplify $\sqrt { 1+{ \left( \cfrac { { x }^{ 4 } }{ -2{ x }^{ 2 } }  \right)  }^{ 2 } } $

  1. $\cfrac { { x }^{ 4 }+1 }{ 2{ x }^{ 2 } } $

  2. $\cfrac{\sqrt{{x}^{2}+1}}{2}$

  3. $\cfrac{{x}^{4}+2{x}^{2}-1}{2{x}^{2}}$

  4. $\cfrac { { x }^{ 4 }-1 }{ 2{ x }^{ 4 } } $


Correct Option: B
Explanation:

$\sqrt{1+(\dfrac{x^4}{-2x^2})^2}$


$\Rightarrow \sqrt{1+\dfrac{x^8}{4x^4}}$

$\Rightarrow \sqrt{\dfrac{4x^4+x^8}{4x^4}}$

$\Rightarrow \dfrac{\sqrt{4x^4+x^8}}{2x^2}$

$\Rightarrow\cfrac{\sqrt{{x}^{2}+1}}{2}$

The equation $2x^4-9x^3+14x^2-9x+2=0$ is of the type

  1. Quadratic equation

  2. Linear equation

  3. Reciprocal Equation

  4. None


Correct Option: C
Explanation:

Given equation is $2x^4-9x^3+14x^2-9x+2=0$ .... $(i)$

The maximum power of $x$ in this equation is $ 4$, so this is $4th$ degree equation  
So, it is neither linear nor quadratic equation.
In reciprocal equation $ ax^4 +bx^3 +cx^2 +dx +e = 0 $, the multiplication of the roots i.e ($\dfrac{e}{a}$) should be  $1$

In the given equation $(i)$, $\dfrac{e}{a}  = \dfrac{2}{2}$  
So the multiplication of roots is equal to one
Therefore, equation $(i)$ is a reciprocal equation.

Hence, option C is correct.

What is a reciprocal equation?

  1. It involves reciprocal of the given variable.

  2. It involves square of the given variable.

  3. It involves squareroot of the given variable.

  4. It involves square and reciprocal of the given variable.


Correct Option: A
Explanation:

Reciprocal is said to be divide $1$ by a number. Reciprocal equation involves reciprocal of the given number.

Determine the root of the equation: $\dfrac{9}{x}-\dfrac{7}{x}=1$

  1. $x=2$

  2. $x=-2$

  3. $x=1$

  4. None of these


Correct Option: A
Explanation:

Given reciprocal equation can be written as

$\dfrac{9}{x}=\dfrac{7+x}{x}$
Cancelling out the denominator on both side, we get
$9=7+x$
$\Rightarrow x=2$
Hence, option A is correct.

Which of the following is not a reciprocal function?

  1. $f(x)=\dfrac{1}{x}$

  2. $f(x)={x}^{-1}$

  3. $f(x)=x$

  4. None of the above


Correct Option: C
Explanation:

This is the reciprocal function:

$f(x)=\dfrac {1}{x}$
Its domain is the real numbers, except $0$, because $\dfrac {1}{0}$ is undefined.
The reciprocal function can also be written as an exponent.
$f(x)=x^{-1}$

$\cfrac { \left( 2x-1 \right) { \left( x-1 \right)  }^{ 4 }{ \left( x-2 \right)  }^{ 4 } }{ (x-2){ \left( x-4 \right)  }^{ 4 } } \le 0$

  1. $(\dfrac{1}{2},2)$

  2. $R$

  3. $\phi$

  4. $(1/3,2)$


Correct Option: A
Explanation:

$\dfrac{(2{x}-1)(x-1)^{4}(x-2)^{4}}{(x-2)(x-4)^{4}} \le 0\implies x\neq 2$


$(2{x}-1)(x-1)^{4}(x-2)^{3}\le 0$


$(x-\dfrac{1}{2})(x-2)^{3}\le 0$

$x\in \bigg(\dfrac{1}{2},2\bigg)$

If $b$ is a root of a reciprocal equation, $f(x)=0$, then another root of $f(x)=0$ is:

  1. $\dfrac{-1}{b}$

  2. $\dfrac{1}{b^2}$

  3. $\sqrt b$

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


Correct Option: D
Explanation:

A reciprocal equation is an equation whose roots can be divided into pairs of numbers, each the reciprocal of the other. 

(equivalently) an equation which is unchanged if the variable $x$ is replaced by its reciprocal $\dfrac{1}{x}$ is reciprocal equation.
Since one root is $b$, then the other root is $\dfrac{1}{b}$

Hence, option D is correct.

A ............ equation is one which remains the same when $x$ is replaced by $\dfrac{1}{x}$.

  1. Reciprocal equation

  2. Radical equation

  3. Exponential equation

  4. Linear equation


Correct Option: A
Explanation:

(Originally) an equation whose roots can be divided into pairs of numbers, each the reciprocal of the other is called Reciprocal equation

(Equivalently) an equation which is unchanged if the variable $x$ is replaced by its reciprocal $\dfrac{1}{x}$ is known as reciprocal equation.
Hence, option A is correct.

The roots of equation $2x^4-9x^3+14x^2-9x+2=0$ are

  1. $(1,2,3,4)$

  2. $\left(1,1,\dfrac{1}{2},2\right)$

  3. $\left(1,\dfrac{1}{3},3,1\right)$

  4. $\left(0,1,1,\dfrac{1}{2}\right)$


Correct Option: B
Explanation:

We can see that in the giving equation, the multiplication of roots is $1$ 

i.e multiplication of roots $=\dfrac{e}{a}$ in the equation $ax^4 +bx^3 + cx^2 +dx  +e  =0$  
$\Rightarrow $ $\dfrac{e}{a}  = \dfrac{2}{2}  = 1 $
Now, sum of the roots is $\dfrac{-b}{a}  = -(\dfrac{-9}{2}) =  \dfrac{9}{2}$

$\Rightarrow $ it is only possible in option B.
Hence, option B is correct.

The domain of reciprocal equation is :

  1. $R$

  2. $R-{0}$

  3. $Q$

  4. $R^+$


Correct Option: B
Explanation:

We know that in reciprocal equation, if one value of $x$ is $a$ then the other value of $x$  will be $\dfrac{1}{a}$

But, if $a = 0$ then $\dfrac{1}{a}$ does not exist  

Therefore, $0$ can not be in the domain of a reciprocal equation.
So, domain of reciprocal equation will be set of all real numbers excluding $0$.
Hence, option B is correct.

The range of reciprocal equation is:

  1. $R$

  2. $R-{0}$

  3. $R^+$

  4. $Q$


Correct Option: B
Explanation:

The range is defined as the set of all output values or the set of all those possible values which appear on Y axis in the graph of given function. 

The domain and range of a reciprocal function are all the real number except for zero. 
This is because reciprocal of $0$ i.e. is undefined.
The range of reciprocal equation is $R-0$

The solution set of the equation 
$x^{2/3} + x^{1/3} = 2 $ is

  1. ${-8, 1}$

  2. ${8, 1}$

  3. ${1, -1}$

  4. ${2, -2}\$


Correct Option: A
Explanation:

Let ${ x }^{ \cfrac { 1 }{ 3 }  }=t\ { t }^{ 2 }+t-2=0\ { t }^{ 2 }+2t-t-2=0\ t(t+2)-(t+2)=0\ (t-1)(t+2)=0\ t=1\ x^{ \cfrac { 1 }{ 3 }  }=1\ x=1\ t=-2\ x^{ \cfrac { 1 }{ 3 }  }=-2\ x=-8\ x=\left( -8,1 \right)$

Identify which of the following are reciprocal equations of 1st type.

  1. $2x^4+5x^3+2x^2+5x-2=0$

  2. $2x^4-5x^3+2x^2-5x+2=0$

  3. $2x^4-5x^3+2x^2+5x-2=0$

  4. None of the above


Correct Option: B
Explanation:

Reciprocal equation is the equation which have even numbers of roots and if one root is $x$ then the other root will be $\dfrac{1}{x}$ and the multiplication of all roots will be one.

Now $1st$ type = where cofficients  $a=e$ in 4th order equation  $ax^4 +bx^3 +cx^{2}  + dx+e = 0 $

In option [A]  $a =2$  and $e = -2$  not $1st$ type

In option [B]  $a =2$  and $e = 2$  this is a $1st$ type reciprocal equation 

In option [C]  $a =2$  and $e = -2$  not a $1st$ type reciprocal equation.
Hence, B is correct.

Identify if the following equation is a reciprocal equation by rearranging.

  1. $2(x^4+1)+89x^2= 56x(x^2+1)$

  2. $2(x^4+1)+89x^2= 56x(x+1)$

  3. $2(x^4+1)+89x^2= 56x^2(x+1)$

  4. None of these


Correct Option: D
Explanation:

To be reciprocal equation, the multiplication of the roots $(\dfrac{e}{a})$ should be $1$ 

(A)
After rearranging the equation 
$\Rightarrow $   $2x^4 -56x^3 +89x^2 -56x +2 = 0 $
$\Rightarrow $  $\dfrac{e}{a} = \dfrac{2}{2}  = 1 $
So, multiplication of roots is $1$  
Thus, it is an reciprocal equation 

(B)
$2x^4 -33x^2 -56x +2 = 0 $

$\Rightarrow $  $\dfrac{e}{a} = \dfrac{2}{2}  = 1 $

So, multiplication of roots is $1$  
Thus, it is an reciprocal equation 


(C)

$\Rightarrow $   $2x^4 -56x^3 +33x^2 +2 = 0 $

$\Rightarrow $  $\dfrac{e}{a} = \dfrac{2}{2}  = 1 $

So, multiplication of roots is $1$  
Thus, it is an reciprocal equation.

Hence, the answer is option D.

$2x^4-3x^3+7x^2+3x-2=0$ is not a reciprocal equation, because

  1. The coefficients from beginning to end and vice versa are not the same.

  2. All the coefficients of terms are not same

  3. The coefficients from beginning to end and vice versa are same.

  4. None of these


Correct Option: A
Explanation:

Here, the coefficients are not palindromic because the first and and last coefficients are opposite in sign , same is the case for second last and second coefficient.

The Equation $5x^4-3x^3+7x^2-4x+2=0$ is of the type

  1. Quadratic

  2. Linear

  3. Reciprocal

  4. None


Correct Option: D
Explanation:

The highest power of $x $ in this equation is $4$, so this is a $4th$ order equation.

Thus, it is neither linear nor quadratic.
Now to be reciprocal equation the multiplication of roots should be $1$  and in the given equation 
Multiplication of roots is $\dfrac{e}{a}=\dfrac{2}{5}$
So this not a reciprocal equation 
Hence, option D is correct.

The inverse of the function $f(x) = \frac{{{e^x} - {e^{ - x}}}}{{{e^x} + {e^{ - x}}}}$ is

  1. $\dfrac{1}{2}\ell n\dfrac{{1 + x}}{{1 - x}}$

  2. $\dfrac{1}{2}\ell n\dfrac{{2 + x}}{{2 - x}}$

  3. $\dfrac{1}{2}\ell n\dfrac{{1 - x}}{{1 + x}}$

  4. $2\ell n(1 + x)$


Correct Option: A
Explanation:

$y=\cfrac { { e }^{ x }-{ e }^{ -x } }{ { e }^{ x }+{ e }^{ -x } }$

$y=\cfrac { \cfrac { { e }^{ 2x }-1 }{ { e }^{ x } }  }{ \cfrac { { e }^{ 2x }+1 }{ { e }^{ x } }  }$
 $y=\cfrac { { e }^{ 2x }-1 }{ { e }^{ 2x }+1 }$
 for universe replace;$x$ with $y$
$\cfrac { x }{ 1 } =\cfrac { { e }^{ 2y }-1 }{ { e }^{ 2y }+1 }$
 using componendo divodendo
 $\cfrac { x+1 }{ x-1 } =\cfrac { { e }^{ 2y }-1+{ e }^{ 2y }+1 }{ { e }^{ 2y }-1-{ e }^{ 2y }-1\quad  }$
 $\cfrac { x+1 }{ x-1 } =-\cfrac { 2{ e }^{ 2y } }{ 2 }$
 $\cfrac { 1+x }{ 1-x } ={ e }^{ 2y }$
$\left(\cfrac { 1+x }{ 1-x } \right)=2y$
$ y=\cfrac { 1 }{ 2 } ln\left(\cfrac { 1+x }{ 1-x } \right)$

If $ax^{3}+bx^{2}+cx+d=0$ is a reciprocal equation of the first type, then 

  1. $a=d,b=c$

  2. $a=c,b=d$

  3. $a=-d,b=-c$

  4. $a=-c,b=-d$


Correct Option: A
Explanation:

If $ax^3+bx^2+cx+d$ is a reciprocal equation of the first type,

We know that

$a _{r}=a _{n-r}$ where $a _{n}$ are the coefficient of the equation $f(x)$

So, as $f(x)=ax^3+bx^2+cx+d$

$a=d$ and $ b=c$

If $f(x)=1+\displaystyle \int^{x} _{0}t^{2}f(t)dt$, then the number of solution of $f(x)=x^{2}+1$ is

  1. $1$

  2. $2$

  3. $3$

  4. $4$


Correct Option: A

The equation of the line, reciprocal of whose intercepts on the axes are $a$ and $b$ given by

  1. $\dfrac x 2$ + $\dfrac yb$ = $1$

  2. $ax + by = 1$

  3. $ax + by = ab$

  4. $ax = by = 1$


Correct Option: B
Explanation:

Let A & B be the part of intersection of line with X & Y axis respectively.

$\Rightarrow A= \left(\cfrac {1}{a},0\right)$
$\Rightarrow B= \left(0,\cfrac {1}{b}\right)$
$\therefore$ Equation of line= $\left(y-\cfrac {1}{b}\right)=\left(\cfrac {\cfrac {1}{b}-0}{0-\cfrac {1}{a}}\right)$
$\Rightarrow \left(\cfrac {1}{a}\right)\left(y-\cfrac {1}{b}\right)=\cfrac {1}{b}x$
$\Rightarrow \cfrac {-y}{a}+\cfrac {1}{ab}= \cfrac {x}{b}$
$\Rightarrow \cfrac {x}{b}+\cfrac {y}{a}=\cfrac {1}{ab}$
$\Rightarrow ax+by=1$

The equation $\sin^{-1}x-3\sin^{-1}a=0$ has real solutions for x if?

  1. $a \in R$

  2. $a \in [-1, 1]$

  3. $a \in \left[0, \dfrac{1}{2}\right]$

  4. $a \in \left[-\dfrac{1}{2}, \dfrac{1}{2}\right]$


Correct Option: A

The root(s) of the reciprocal equation of second type and of even degree is/are

  1. $x=1$

  2. $x=-1$

  3. $x=\pm1$

  4. $x=0$


Correct Option: C
Explanation:
$x = -1$ is a root of the reciprocal equation of first type and of odd degree. 
$x = 1$ is a root of the reciprocal equation of second type and of odd degree.
$x=±1$ are two roots of reciprocal equation of second type and of even degree. 

lf $\mathrm{f}({x})=0$ is a reciprocal equation of second type and even degree, then a factor of $\mathrm{f}({x})$  is:

  1. $x+1$

  2. $x-1$

  3. $x^{2}-1$

  4. $x^{2}$


Correct Option: A,B,C
Explanation:

The equation will have 2 solutions, 1 and -1.
The solution will be x+1 and x-1,
$(x-1)(x+1)=x^2-1$

The equation whose roots are the reciprocal of the roots of $2x^2 - 3x -5=0$, is:

  1. $5x^2+3x-2=0$

  2. $2x^2+3x-5=0$

  3. $3x^2-3x+2=0$

  4. $2x^2+5x -3 = 0$


Correct Option: A
Explanation:

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


$\Rightarrow (x+1)(2x-5)=0$

$\therefore \alpha=-1$ and $\beta=\dfrac{5}{2}$

Reciprocal of these roots, $\alpha=-1$ and $\beta=\dfrac{2}{5}$

General form of quadratic equation $x^2-(\alpha+\beta)x+\alpha\beta=0$

$\Rightarrow x^2-(-1+\dfrac{2}{5})x-\dfrac{2}{5}=0$

$\Rightarrow 5x^2+3x-2=0$

The root of the reciprocal equation of first type and of odd degree is:

  1. $x= 1$

  2. $x=-1$

  3. $x=\pm1$

  4. $x=0$


Correct Option: B
Explanation:
$x = -1$ is a root of the reciprocal equation of first type and of odd degree. 
$x = 1$ is a root of the reciprocal equation of second type and of odd degree.
$x=±1$ are two roots of reciprocal equation of second type and of even degree. 

If the reciprocal of every root of an equation is also a root of it, then the equation is said to be a

  1. reciprocal equation of first type

  2. reciprocal equation of second type

  3. reciprocal equation

  4. None of these


Correct Option: C
Explanation:

An equation whose roots can be divided into pairs of numbers, each the reciprocal of the other or aequation which is unchanged if the variable is replaced by its reciprocal is known as reciprocal euation.

lf $\mathrm{f}(\mathrm{x})=0$ is a reciprocal equation of first type and odd degree, then a factor of $\mathrm{f}(\mathrm{x})$ is:

  1. $\mathrm{x}-2$

  2. $\mathrm{x}-1$

  3. $\mathrm{x}$

  4. $\mathrm{x}+1$


Correct Option: D
Explanation:

When the reciprocal equation is of an odd degree, $x=-1$ is always a solution.
So, $x+1$ is a factor.

The root of the reciprocal equation of second type and of odd degree is:

  1. $x=-1$

  2. $x=+1$

  3. $x=\pm1$

  4. $x=0$


Correct Option: B
Explanation:
$x = -1$ is a root of the reciprocal equation of first type and of odd degree. 
$x = 1$ is a root of the reciprocal equation of second type and of odd degree.
$x=±1$ are two roots of reciprocal equation of second type and of even degree. 

lf $\mathrm{f}({x})=0$ is a reciprocal equation of second type and fifth degree, then a root of $\mathrm{f}({x})=0$  is:

  1. $0$

  2. $1$

  3. $-1$

  4. $2$


Correct Option: B
Explanation:

When the reciprocal equation is of an odd degree, second type, $x=1$ is always a solution.

The roots equation $x^4-3x^3+4x^2-3x+1=0$ is 

  1. $0$

  2. $1$

  3. $2$

  4. $3$


Correct Option: B
Explanation:

$x^4-3x^3+4x^2-3x+1=0$
This equation is resiprocal equation of first type as $a _{n-i}=a _i$
Dividing equation by $x^2$:
$x^2-3x+4-\dfrac3x+\dfrac{1}{x^2}=0$
$x^2+\dfrac{1}{x^2}-3x-\dfrac3x+4=0$
$\left(x+\dfrac1x\right)^2-2-3\left(x+\dfrac1x\right)+4=0$
$\left(x+\dfrac1x\right)^2-3\left(x+\dfrac1x\right)+2=0$
Let $x+\dfrac1x=y$
$y^2-3y+2=0$
$(y-1)(y-2)=0$
$y=1$ or $y=2$
For $y=1$:
 $x+\dfrac1x=1$
$x^2-x+1=0$
$D=(-1)^2-4(1)(1)=-3<0$
Hence no real value of x exists for this case.
For $y=2$:
$x+\dfrac1x=2$
$x^2-2x+1=0$
$(x-1)^2=0$
$x=1$
Hence solution of the given equation is x=1.

If the coefficients from one end of an equation are equal in magnitude and sign to the coefficients from the other end, then the equation is said to be 

  1. reciprocal equation of second type

  2. reciprocal equation of first type

  3. reciprocal equation

  4. None of these


Correct Option: B
Explanation:


Solve $(1-a^2)(x+a)-2a(1-x^2)=0$

  1. $x= a,\dfrac{-(1+a^2)}{2a}$

  2. $x= 0,\dfrac{-(1+a^2)}{2a}$

  3. $x= 0,\dfrac{-(1+a^2)}{4a}$

  4. $x= 2a,\dfrac{-(1+a^2)}{4a}$


Correct Option: A
Explanation:

Given, $(1-a^2)(x+a)-2a(1-x^2)=0$

$x+a-a^2x-a^3-2a+2ax^2=0$
$x-a-a^2x-a^3+2ax^2=0$
$2ax^2+x(1-a^2)-(a+a^3)=0$
By using formula, we have
$x=\dfrac {-(1-a^2)\pm \sqrt {(1-a^2)^2-4(2a)[-(a+a^3)]}}{2(2a)}$
$=\dfrac {-(1-a^2)\pm \sqrt {(1+3a^2)^2}}{4a}$
$=\dfrac {-(1-a^2)\pm (1+3a^2)}{4a}$
$=\dfrac {-1+a^2+1+3a^2}{4a}; \dfrac {-1+a^2-1-3a^2}{4a}$
$=\dfrac {4a^2}{4a}; \dfrac {-2-2a^2}{4a}$
$=a; \dfrac {-(1+a^2)}{2a}$

Solve the reciprocal equation $x^4-3x^3+4x^2-3x+1=0$

  1. $0$

  2. $1$

  3. $3$

  4. $-1$


Correct Option: B
Explanation:

We see that it is a reciprocal equation, so we divide it by $x^2$: 


$\Rightarrow$$x^2-3x+4-\dfrac{3}{x}+\dfrac{1}{x^2}=0$


$\Rightarrow$$(x^2+\dfrac{1}{x^2})-3(x+\dfrac{1}{x})+4=0$


We will now substitute $x+\dfrac{1}{x}=u$

By squaring it, and solve further we get

$\Rightarrow$$x^2+\dfrac{1}{x^2}=u^2-2$

We plug back into the equation to get

$\Rightarrow$$u^2-3u+2=0$

The solutions are $u _{1}=1, u _{2}=2$
So either $x+\dfrac{1}{x}=1$ or $2$

From the first solution we get 
$\Rightarrow$$x^2-x+1=0$    which has no solution
From the second one we get
$\Rightarrow$$x^2-2x+1=0$ 
$\Rightarrow$$x=1$

If the coefficients from one end of an equation are equal in magnitude and opposite in sign to the coefficients from the other end, then the equation is said to be 

  1. reciprocal equation of second type

  2. reciprocal equation of first type

  3. reciprocal equation

  4. None of these


Correct Option: A
Explanation:
Consider a general equation:

$a _{n}x^n+a _{n-1}x^{n-1}+a _{n-2}x^{n-2}+....................+a _1x+a _0=0$

Now if  $a _n-i=-a _i ,$        $  i=0,1,2,3,...........n$

Then this type of equation is called as reciprocal equation of second type.

Ex- $4x^4-9x^3+9x-4=0$

An equation of the form $2x^4-3x^3+7x^2-3x+2=0$ is called a .................

  1. Reciprocal equation

  2. Radical equation

  3. Exponential equation

  4. Quadratic equation


Correct Option: A
Explanation:

As 'The coefficients from beginning to end and vice versa are the same'
therefore given equation is a reciprocal equation.

Solve for $x$:   $\dfrac{8\sqrt{x-5}}{3x-7}=\dfrac{\sqrt{3x-7}}{x-5}$

  1. $13$

  2. $23$

  3. $14$

  4. $-13$


Correct Option: A
Explanation:

$\cfrac{8\sqrt{x-5}}{3x-7}=\cfrac{\sqrt{3x-7}}{x-5}$

$\Rightarrow 8(x-5)^{\tfrac 32}=(3x-7)^{\tfrac 32}$
Squaring on both sides we get,
$\Rightarrow 64(x-5)^{3}=(3x-7)^{3}$
Taking cube roots on both sides, we get
$\Rightarrow 4(x-5)=(3x-7)$
$\Rightarrow 4x-20=3x-7$
$\Rightarrow x=13$
Hence, option A is correct.

Find $x$,  $2^{x^2}:2^{2x}=8:1$

  1. $3,-1$

  2. $3,1$

  3. $-3,-1$

  4. $-3,1$


Correct Option: A
Explanation:

Given, $2^{x^2}:2^{2x}=8:1$

$\Rightarrow \dfrac {2{x^2}}{2^{2x}}=\dfrac {8}{1}$
$\Rightarrow 2^{x^2}=8.2^{2x}$
$\Rightarrow 2^{x^2}=2^3.2^{2x}$
$\Rightarrow 2^{x^2}=2^{2x+3}$
$\Rightarrow x^2=2x+3$ ....As bases are equal, powers must be equal
$\Rightarrow x^2-2x-3=0$
$\Rightarrow (x-3)(x+1)=0$
$\therefore x=3,-1$

Solve the equation: $x^{-2}-2x^{-1}=8$

  1. $\dfrac{3}{4}, \dfrac{-1}{2}$

  2. $\dfrac{1}{4}, \dfrac{-1}{3}$

  3. $\dfrac{1}{3}, \dfrac{-1}{2}$

  4. $\dfrac{1}{4}, \dfrac{-1}{2}$


Correct Option: D
Explanation:

Given, $x^{-2}-2x^{-1}=8$

$\Rightarrow \dfrac {1}{x^2}-\dfrac {2}{x}=8$
$\Rightarrow \dfrac {1-2x}{x^2}=8$
$\Rightarrow 1-2x=8x^2$
$\Rightarrow 8x^2+2x-1=0$
$\Rightarrow (2x+1)(4x-1)$
$\Rightarrow x=\dfrac {1}{4}, \dfrac {-1}{2}$

The number of solutions $(x, y, z)$ to the system of equations $ x + 2y + 4z = 9, 4yz + 2xz + xy = 13, xyz = 3 $ such that at least two of $ x, y, z$ are integers is

  1. $3$

  2. $5$

  3. $6$

  4. $4$


Correct Option: B
Explanation:
Let the roots of the system equation are:
$\alpha =x,\beta =2y,\gamma =4z$
$\alpha +\beta +\gamma =x+2y+4z=9$
$\alpha \beta +\beta \gamma +\gamma \alpha =2xy+8yz+yzx$
$=2(4yz+2xz+xy)\Rightarrow 26$
$\alpha \beta \gamma =8xyz\Rightarrow 24$
Thus,our polynomial should be:
$P^{3}-9P+26P-24=0$
$(P-2)(P-3)(P-4)=0$
since our roots are :
$\alpha =x,\beta =2y$ and $\gamma =4z$
$(x,2y,4z)=(2,3,4)$ or its permutations,or 6 combination.
However,note that one case if,
$x=4,2y=3$ and $4z=2$
$(x,y,z)=(4,\dfrac{3}{2},\dfrac{1}{2})$
which two of the roots are not an integer :Excluding of this case ,we have five solutions.

Solve the equation $\sqrt{4x^2-7x-15}-\sqrt{x^2-3x}=\sqrt{x^2-9}$

  1. $2, 3$

  2. $1, 6$

  3. $-1, 3$

  4. $1, 3$


Correct Option: D
Explanation:

Given equation is $\sqrt { 4{ x }^{ 2 }-7x-15 } =\sqrt { { x }^{ 2 }-9 } +\sqrt { { x }^{ 2 }-3x } $

$\Rightarrow \sqrt { x-3 } (\sqrt { 4x+5 } )=\sqrt { x-3 } (\sqrt { x+3 } +\sqrt { x } )$
Therefore $x=3$ is one solution and $\sqrt { 4x+5 } =\sqrt { x+3 } +\sqrt { x } $
By squaring above equation on both sides , we get $x+1=\sqrt{x(x+3)}$
Again square it on both sides , we get $x^{2}+2x+1=x^{2}+3x$
$\Rightarrow x=1$
Therefore option $D$ is correct

The roots of $a _ { 1 } x ^ { 2 } + b _ { 1 } x + c _ { 2 } = 0$ are reciprocal of the roots of the equation $a _ { 2 } x ^ { 2 } + b _ { 2 } x + c _ { 2 } = 0$

  1. $\dfrac { a _ { 1 } } { a _ { 2 } } = \dfrac { b _ { 1 } } { b _ { 2 } } = \dfrac { c _ { 1 } } { c _ { 2 } }$

  2. $\dfrac { b _ { 1 } } { b _ { 2 } } = \dfrac { c _ { 1 } } { a _ { 2 } } = \dfrac { a _ { 1 } } { c _ { 2 } }$

  3. $\dfrac { a _ { 1 } } { a _ { 2 } } = \dfrac { b _ { 1 } } { c _ { 2 } } = \dfrac { c _ { 1 } } { b _ { 2 } }$

  4. $a _ { 1 } = \dfrac { 1 } { a _ { 2 } } , b _ { 1 } = \dfrac { 1 } { b _ { 2 } } , c _ { 1 } = \dfrac { 1 } { c _ { 2 } }$


Correct Option: B
Explanation:
Given:${a} _{1}{x}^{2}+{b} _{1}x+{c} _{1}=0$     ........$(1)$
${a} _{2}{x}^{2}+{b} _{2}x+{c} _{2}=0$     ........$(2)$

Let $\alpha,\,\beta$ be the roots of ${a} _{1}{x}^{2}+{b} _{1}x+{c} _{1}=0$     ........$(1)$

$\Rightarrow\,\alpha+\beta=-\dfrac{{b} _{1}}{{a} _{1}}$ and 

$\alpha\beta=\dfrac{{c} _{1}}{{a} _{1}}$

Given:Roots of $(1)$ are reciprocal to $(2)$

$\dfrac{1}{\alpha}+\dfrac{1}{\beta}=-\dfrac{{b} _{2}}{{a} _{2}}$ and $\dfrac{1}{\alpha\beta}=\dfrac{{c} _{2}}{{a} _{2}}$

$\Rightarrow\,\dfrac{\alpha+\beta}{\alpha\beta}-\dfrac{{b} _{2}}{{a} _{2}}$ and $\dfrac{1}{\alpha\beta}=\dfrac{{c} _{2}}{{a} _{2}}$

Using $\alpha+\beta=-\dfrac{{b} _{1}}{{a} _{1}}$ and $\alpha\beta=\dfrac{{c} _{1}}{{a} _{1}}$ we have

$\Rightarrow\,\dfrac{-\dfrac{{b} _{1}}{{a} _{1}}}{\dfrac{{c} _{1}}{{a} _{1}}}=-\dfrac{{b} _{2}}{{a} _{2}}$ and $\dfrac{1}{\dfrac{{c} _{1}}{{a} _{1}}}=\dfrac{{c} _{2}}{{a} _{2}}$

$\Rightarrow\,\dfrac{-{b} _{1}}{{c} _{1}}=-\dfrac{{b} _{2}}{{a} _{2}}$ and
 
$\dfrac{{a} _{1}}{{c} _{1}}=\dfrac{{c} _{2}}{{a} _{2}}$

$\Rightarrow\,\dfrac{{b} _{1}}{{b} _{2}}=\dfrac{{c} _{1}}{{a} _{2}}$ and 

$\dfrac{{a} _{1}}{{c} _{1}}=\dfrac{{c} _{2}}{{a} _{2}}$

$\Rightarrow\,\dfrac{{b} _{1}}{{b} _{2}}=\dfrac{{c} _{1}}{{a} _{2}}$ and 

$\dfrac{{c} _{1}}{{a} _{1}}=\dfrac{{a} _{2}}{{c} _{2}}$

$\Rightarrow\,\dfrac{{b} _{1}}{{b} _{2}}=\dfrac{{c} _{1}}{{a} _{2}}$ and 

$\dfrac{{c} _{1}}{{a} _{2}}=\dfrac{{a} _{1}}{{c} _{2}}$

$\therefore\,\dfrac{{b} _{1}}{{b} _{2}}=\dfrac{{c} _{1}}{{a} _{2}}=\dfrac{{a} _{1}}{{c} _{2}}$

Option$(b)$ is correct.
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