0

Distance from a point to line - class-XII

Description: distance from a point to line
Number of Questions: 40
Created by:
Tags: vectors, lines and planes three dimensional geometry straight lines maths product of vectors vectors: lines in two and three dimensions
Attempted 0/40 Correct 0 Score 0

The length of the perpendicular drawn from the points $(5,4,-1)$ to the line $\overline r  = \widehat i + \lambda \left( {2\widehat i + 9\widehat i + 5\widehat k} \right)$ is

  1. $\dfrac{{\sqrt {2190} }}{{110}}$

  2. $\sqrt { \frac { { 2199 } }{ { 110 } }  } $

  3. $\sqrt { \frac { { 2109 } }{ { 110 } }  } $

  4. $\dfrac{{\sqrt {23190} }}{{110}}$


Correct Option: C
Explanation:

According to the question:

$\begin{array}{l} let\, the\, point\, (5,4,-1)\, \, be\, \, P\, and\, the\, point\, through\, which\, the\, \, line\, passes\, \, be\, \, Q\, (1,0,0).\, \, \, \,  \ the\, line\, is\, parallel\, to\, the\, vector:\, \, \overrightarrow { r } =\left( { 2\hat { i } +9\hat { i } +5\hat { k }  } \right)  \ Now, \ \overrightarrow { PQ } =-4\hat { i } -4\widehat { j } +\hat { k }  \ \therefore \, \, \, \overrightarrow { r\,  } \, \times \overrightarrow { PQ } =\left| \begin{array}{l} \, \, \hat { i } \, \, \, \, \, \, \, \, \, \, \, \, \, \, \widehat { j } \, \, \, \, \, \, \, \, \, \, \, \widehat { k }  \ \, \, 2\, \, \, \, \, \, \, \, \, \, \, \, \, \, 9\, \, \, \, \, \, \, \, \, \, \, 5\, \,  \ \, -4\, \, \, \, \, \, \, -4\, \, \, \, \, \, \, \, \, \, 1 \end{array} \right| \, \, \, \, \, \, \, \,  \ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, =\, 29\, \hat { i } \, -\, \, 22\, \widehat { j } \, +28\, \widehat { k }  \ \Rightarrow \left| { \, \overrightarrow { r\,  } \, \times \overrightarrow { PQ }  } \right| =\sqrt { \, { { (29) }^{ 2 } }\, +{ { (-\, \, 22) }^{ 2 } }\, +{ { (28) }^{ 2 } } }  \ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, =\sqrt { 841+484+784 } =\sqrt { 2109 }  \ \left| { \overrightarrow { r\,  } \,  } \right| =\sqrt { { 2^{ 2 } }+{ 9^{ 2 } }+{ 5^{ 2 } } }  \ \, \, \, \, \, \, \, =\sqrt { 4+81+25 } =\sqrt { 110 }  \ d=\frac { { \, \left| { \overrightarrow { r\,  } \, \times \overrightarrow { PQ }  } \right|  } }{ { \left| { \overrightarrow { r\,  } \,  } \right|  } } =\frac { { \sqrt { 2109 }  } }{ { \sqrt { 110 }  } } =\sqrt { \frac { { 2109 } }{ { 110 } }  }  \ so\, that\, the\, correct\, option\, is\, C. \end{array}$

The perpendicular distance of the point $(2,4,-1)$ from the line $\dfrac{x+5}{1}=\dfrac{y+3}{4}=\dfrac{z-6}{-9}$ is

  1. $3$

  2. $5$

  3. $7$

  4. $9$


Correct Option: C
Explanation:
Let P(2,4,1)P(2,4,−1) be the given point and the Line Lx51=y34=z69=λL→x−51=y−34=z−6−9=λ
d.r.⇒d.r. of the line L=(1,4,9)L=(1,4,−9)
Any point Q(x,y,z)Q(x,y,z) on the line L is given by Q(λ+5,4λ+3,9λ+6)Q(λ+5,4λ+3,−9λ+6)
Let this point QQ be the foot of  of the point P on the line LL.
d.r of $\overrightarrow {PQ} $ the 
=(λ+52,4λ+34,9λ+6+1)=(λ+5−2,4λ+3−4,−9λ+6+1)
=(λ+3,4λ1,9λ+7)
$\overrightarrow {PQ} $(1,4,9)=0∴PQ¯.(1,4,−9)=0
(λ+3,4λ1,9λ+7).(1,4,9)=0(λ+3,4λ−1,−9λ+7).(1,4,−9)=0
(λ+3)1+(4λ1)49(9λ+7)=0⇒(λ+3)1+(4λ−1)4−9(−9λ+7)=0
λ+3+16λ4+81λ63=0⇒λ+3+16λ−4+81λ−63=0
98λ=64⇒98λ=64
λ=3249
$\overrightarrow {PQ} $ is  to the line L
Substituting λλ in Q we get the foot of Q⊥Q as
Q(3249Q(3249+5,12849+5,12849+3,28849+3,−28849+6)+6)

 distance$\overrightarrow {PQ} $ =7



A point on the line $\bar {r}=2\hat {i}+3\hat {j}+4\hat {k}+t(\hat {i}+\hat {j}+\hat {k})$ is

  1. $(2014,2015,2016)$

  2. $(2013,2015,2017)$

  3. $(2013,2014,2017)$

  4. $None\ of\ these$


Correct Option: A

Perpendicular distance between the plane $  2 x-y+2 z=1  $ and origin is 

  1. $ \frac{1}{3} $

  2. $3$

  3. $ \frac{1}{6} $

  4. $6$


Correct Option: A
Explanation:

The perpendicular distance of a plane and origin is give as 

$\dfrac{|d|}{\sqrt {a^2+b^2+c^2}}\\dfrac{1}{\sqrt {2^2+1^2+2^2}}\\dfrac 1{\sqrt 9}=\dfrac 13$

The position vector of point $A$ is $(4, 2, -3)$. If $p {1}$ is perpendicular distance of $A$ from $XY-plane$ and $p _{2}$ is perpendicular distance from Y-axis, then $p _{1} + p _{2} =$ ______.

  1. $8$

  2. $3$

  3. $2$

  4. $7$


Correct Option: A
Explanation:

$P _1$ is perpendicular distance of A from XY-plane 
So, $x _1=0,y _1=0,z _=-3$
$\therefore p _1=\sqrt{(-3)^2}=3$
$p _2$ is perpendicular distance from Y-axis
So, $x _1=4,y _1=0,z _1=-3$
$p _{2} = \sqrt {x _{1}^{2} + y _{1}^{2}}$
$\therefore p _2=\sqrt{4^2+(-3^2)}=5$
$p _{1} + p _{2} = 5 + 3 = 8$.

The perpendicular distance from a point $P$ with position vector $5\vec {i}+\vec {j}+3\vec {k} $ to the line $\vec {r}=(3\vec {i}+7\vec {j}+\vec {k})+t(\vec {j}+\vec {k})$ is

  1. $3$

  2. $6$

  3. $9$

  4. $12$


Correct Option: B
Explanation:

Point Pis $(5, 1, 3)$  and line is given

$\vec r = \left( {3\hat i + 7\hat j + \hat k} \right) + t\left( {\hat j + \hat k} \right)$
 let the foot of the perpendicular from point +p to the given line be $\theta \left( {x{,^1}y{,^1},{z^1}} \right)$ then direction ratios of $pq$ are
$\left( {{x^1} - 5,{y^1} - 1,{z^1} - 3} \right)$
since $pq$is $ \bot $ to the given line so 
$b \times \left( {{x^1} - 5} \right) + 1 \times \left( {{y^1} - 11 + 1 \times \left( {{z^1} - 31} \right)} \right) = 0$
${y^1} + 1 + {z^1} - 3 = 0$
${y^1} + {z^1} = 4 = 0$ 
artesian equation of the given line is 
$\frac{{x - 3}}{0} = \frac{{y - 7}}{1} = \frac{{z - 1}}{1}$ 
let $\frac{{x - 3}}{0} = \frac{{y - 7}}{1} = \frac{{z - 1}}{1} = r$
$x=3, y= r+7, z=r+1$
so general point on this line is (3,r+7,r+1)
since $\left( {{x^1},{y^1},{z^1}} \right)$
lies on this line so ${x^1} = 3\,\,{y^1} = r + 7\,\,{z^1} = r + 1$
putting values of ${y^1}& $ in
${y^1} + {z^1} = 4$
$r + 7 + r + 1 = 4$
$2r=-4$
$=r=-2$
thus ${x^1} = 3,{y^1} =  - 2 + 7 = 5$
${z^1} =  - 2 + 1 =  - 1$
so point Q is $(3,5,-1)$
therefore perpendicular distance $\sqrt {{{\left( {5 - 3} \right)}^2} + {{\left( {1 - 5} \right)}^2} + {{\left( {3 + 1} \right)}^2}} $
$\sqrt {4 + 16 + 16} $
$\sqrt {36} $
$=6units$

The perpendicular distance of the point $(6, -4, 4)$ on to the line joining the points $A(2, 1, 2), B(3, -1, 4)$ is?

  1. $1$

  2. $2$

  3. $3$

  4. $4$


Correct Option: C
Explanation:

Let the point be $P(6,-4,4)$ 


Equation of the line joining $A$ and $B$ is 

$\dfrac{x-2}{3-2}=\dfrac{y-1}{-1-1}=\dfrac{z-2}{4-2}$

$\dfrac{{x - 2}}{1} = \dfrac{{y - 1}}{{ - 2}} = \dfrac{{z - 2}}{2}$

Let
$\dfrac{{x - 2}}{1} = \dfrac{{y - 1}}{{ - 2}} = \dfrac{{z - 2}}{2}=r$

$x=r+2,\,y=-2r+1,\,z=2r+2,\,z=2r+2$

General point on the given line is 
$(r+2,-2r+1,2r+2)$

Let the foot of perpendicular from $P$ to the given line be $Q(r _1+2,-2r _1+1,2r _1+2)$

Direction ratios the line $PQ$ are 
$(r _1+2-6,\,-2r _1+1+4,\,2r _1+2-4)$ which is 
$r _1-4,\,\,-2r _1+5,\,\,2r _1-2$

Since the line $PQ$ is perpendicular to the given line 

$1(r _1-2)-2(-2r _1+5)+(2r _1-2)=0$

$r _1=2$

$\begin{array}{l} { r _{ 1 } }+2=4 \  \ -2{ r _{ 1 } }+1=-3 \  \ 2{ r _{ 1 } }+2=6 \end{array}$
Therefore, 
Foot of perpendicular is $Q(4,-3,6)$

Perpendicular distance $=PQ$

$=\sqrt {(4-6)^2+(-3+4)^2+(6-4)^2}=3$

Find point $Q$, the foot of perpendicular drawn on line repeat $AB$, from $P\ A(1, 2, 4)\ B(3, 4,5)\ P(2, 4, 3)$.

  1. $ Q=(\dfrac{19}{9}, \dfrac{28}{9}, \dfrac{41}{9}).$
  2. $Q=(12,20,30).$

  3. $Q=(55,66,44).$

  4. $Q=(23,34,45).$


Correct Option: A
Explanation:
Points are $P(2,4,3), A(1,2,4), B(3,4,5).$ 
To find the foot of the perpendicular from $P$ onto $AB$.

Equation of $AB$
$x = 1+(3-1)t = 1+2t$
$y = 2+(4-2)t = 2+2t$
$z = 4+(5-4)t = 4+t$

Direction Coefficients
$ 2,  2,  1$ $Q$ lies on the $AB.$

Equation of a $3-d$ plane perpendicular to $AB$ 
$2x + 2y + z = C $

This plane passes through $P$
So,
 $2\times 2+2\times 4+3= C$

$Q$ lies on the line and the plane. 
So,
$4t+2 + 4t+4 + t+4 = 15$
So for $Q$ $t = 5/9$
Hence, $Q=(19/9, 28/9, 41/9)$

Hence, this is the answer.

The length of the perpendicular drawn from the point $( 3 , - 1,11 )$ to the line $\dfrac { x } { 2 } = \dfrac { y - 2 } { 3 } = \dfrac { z - 3 } { 4 }  $ is:

  1. $\sqrt { 66 }$

  2. $\sqrt { 29 }$

  3. $\sqrt { 33 }$

  4. $\sqrt { 53 }$


Correct Option: D

The perpendicular distance of $p _1, p _2, p _3$ of points $({a^2}, 2a), \, (ab, a + b), \, ({b^2}, 2b)$ respectively from straight line $x + y\tan \theta + {{tan}^2} \theta = 0$ are in :

  1. A.P

  2. G.P

  3. H.P

  4. None of these


Correct Option: B

The length of the perpendicular drawn from $(1, 2, 3)$ to the line $\dfrac {x-6}{3}=\dfrac {y-7}{2}=\dfrac {z-7}{-2}$ is-

  1. $4$

  2. $5$

  3. $6$

  4. $7$


Correct Option: D
Explanation:

Let us take a point on line $(3\lambda +6,2\lambda +7,-2\lambda +7)$.
Direction ratio's of line which is  perpendicular to given line 
$(3\lambda +6-1,2\lambda +7-2,-2\lambda +7-3)$
$(3\lambda +5,2\lambda +5,-2\lambda +4)$
and the direction ratio's of given line are 3,2,-2
These two lines are perpendicular, so$(3\lambda +5)*3+(2\lambda +5)*2+(-2\lambda +4)+(-2)=0$
$\lambda=-1$
So, point is $(2,4,6)$
So distance between $(3,5,9)$ and $(1,2,3)$ is $7$. (by distance formula)

Distance of the point $P(\vec p)$ from the line $\vec r=\vec a+\lambda \vec b$ is-

  1. $\mid (\vec a-\vec p)+\dfrac {((\vec p-\vec a)\cdot \vec b)\vec b}{\mid \vec b\mid^2}\mid$

  2. $\mid (\vec b-\vec p)+\dfrac {((\vec p-\vec a)\cdot \vec b)\vec b}{\mid \vec b\mid^2}\mid$

  3. $\mid (\vec a-\vec p)+\dfrac {((\vec p-\vec b)\cdot \vec b)\vec b}{\mid \vec b\mid^2}\mid$

  4. None of these.


Correct Option: A
Explanation:

Let $Q(\vec{q})$ be the foot of perpendicular drawn from $P(\vec{p})$ to the line $\vec{r} = \vec{a} + \lambda\vec{b}$
$\Rightarrow (\vec{q}-\vec{p}) \cdot \vec{b} = 0$ and $ \vec{q} = \vec{a} + \lambda\vec{b}$
$\Rightarrow ( \vec{a} + \lambda\vec{b}-\vec{p}) \cdot \vec{b} = 0$
$\Rightarrow ( \vec{a} -\vec{p}) \cdot \vec{b} +  \lambda \mid \vec{b} \mid^2 = 0$
$\Rightarrow   \lambda  = \dfrac{( \vec{p} -\vec{a}) \cdot \vec{b} }{\mid \vec{b} \mid^2}$
$\Rightarrow   \vec{q} -\vec{p} = \vec{a} + \dfrac{( \vec{p} -\vec{a}) \cdot \vec{b} }{\mid \vec{b} \mid^2} - \vec{p}$
$\Rightarrow   \mid \vec{q} -\vec{p}\mid =\mid (\vec{a} - \vec{p})+ \dfrac{( \vec{p} -\vec{a}) \cdot \vec{b} }{\mid \vec{b} \mid^2} \mid$

The distance of the point $P(3,8,2)$ from the line $\cfrac{1}{2}(x-1)=\cfrac{1}{4}(y-3)=\cfrac{1}{3}(z-2)$ measured parallel to the plane $3x+2y-2z+15=0$ is

  1. $7$

  2. $9$

  3. $\sqrt{7}$

  4. $49$


Correct Option: A
Explanation:
Lines equation : $\dfrac{x-1}{2}= \dfrac{y-3}{4} = \dfrac{z-2}{3}= \lambda $
General point $(B)= (2\lambda+1, 4\lambda+3, 3 \lambda+2)$
$\overrightarrow {BP} = (2 \lambda-2, 4 \lambda -5, 3 \lambda)$
As $\overrightarrow {BP}$ is parallel to the plane, it is perpendicular to its normal, $\Rightarrow (2 \lambda - 2, 4\lambda-5, 3\lambda).(3,2,-2)=0$
$\Rightarrow 6 \lambda-6+8 \lambda-10-6 \lambda=0 \Rightarrow 8\lambda=16 \Rightarrow \lambda=2$
$\Rightarrow B= (5,11,8)= |\overrightarrow {BP}|= \sqrt{4+9+36}= \sqrt{49} = 7 \Rightarrow (A)$

The length of the perpendicular from (1,6,3) to the line $\frac{x}{1}=\frac{y-1}{2}=\frac{z-2}{3}$ is 

  1. 3

  2. $\sqrt{11}$

  3. $\sqrt{13}$

  4. 5


Correct Option: C

The shortest distance of the points $(a, b, c)$ from the x-axis is

  1. $\sqrt{(a^2 + b^2)}$

  2. $\sqrt{(b^2 + c^2)}$

  3. $\sqrt{(c^2 + a^2)}$

  4. $\sqrt{(a^2 + b^2 + c^2)}$


Correct Option: B
Explanation:

The point is $(a,b,c)$
the perpendicular distance from $x$ axis will be the shortest distance

$\therefore$ distance is $\sqrt{{b}^{2}+{c}^{2}}$

A line is perpendicular to the plane $x+2y+2z=0$ and passes through $(0, 1, 0)$. The perpendicular distance of this line from the origin is

  1. $\displaystyle \frac {\sqrt 5}{3}$

  2. $\displaystyle \frac {\sqrt 7}{3}$

  3. $\displaystyle \frac {2}{3}$

  4. $3$


Correct Option: A
Explanation:

Since the line is perpendicular to the plane $x+2y+2z=0$, so directon of line will be $(1,2,2)$ and it passes through $(0,1,0)$,
Therefore equation of line is $\dfrac{x}{1}=\dfrac{y-1}{2}=\dfrac{z}{2}$
So general point on the line is $(r,2r+1,2r)$
Now direction ratio of line passing through this point and origin which perpendicular to given line is $(r,2r+1,2r)$
Since they are perpendicular, so dot product will be $0$ .
$r+2\times (2r+1)+2\times 2r{=}0$
$r+4r+2+4r{=}0$
$\therefore r{=}$$\dfrac{-2}{9}$
So points on line which perpendicular from origin is $(-2/9,5/9,-4/9)$
Now applying distance formula,
${=}$ $\sqrt{{(-2/9)}^{2}+{(5/9)}^{2}+{(-4/9)}^{2}}$
${=}$ $\sqrt{4/81+25/81+16/81}$
${=}$ $\dfrac{\sqrt{5}}{3}$

If $(a-a\prime )^2+(b-b\prime )^2+(c-c\prime )^2=p$ and $(ab\prime -a\prime b)^2+(bc\prime -b\prime c)^2+(ca\prime -c\prime a)^2=q,$ then the perpendicular distance of the line $ax+by+cz=1,$ $a\prime x+b\prime y+c\prime z=1$ from origin, is 

  1. $\sqrt { \dfrac { p }{ q } } $

  2. $\sqrt { \dfrac { q }{ p } } $

  3. $\dfrac { p }{ \sqrt { q } } $

  4. $\dfrac { q }{ \sqrt { p } } $


Correct Option: A

The length of the perpendicular drawn from the point $(3,\ -1,\ 11)$ to the line $\dfrac {x}{2}=\dfrac {y-2}{3}=\dfrac {z-3}{4}$

  1. $\sqrt {53}$

  2. $\sqrt {66}$

  3. $\sqrt {29}$

  4. $\sqrt {33}$


Correct Option: A

If $\vec{AB}=\vec{b}$ and $\vec{AC}=\vec{c}$, then the length of perpendicular from $A$ to the line $BC$ is 

  1. $\displaystyle \dfrac{\left | \vec{b}\times \vec{c} \right |}{\left | \vec{b}+\vec{c} \right |}$

  2. $\displaystyle \dfrac{\left | \vec{b}\times \vec{c} \right |}{\left | \vec{b}-\vec{c} \right |}$

  3. $\displaystyle \dfrac{1}{2}\frac{\left | \vec{b}\times \vec{c} \right |}{\left | \vec{b}-\vec{c} \right |}$

  4. None of these


Correct Option: B
Explanation:

Let length of perpendicular be $h$,
Then area of triangle $ABC$ is, 

$=\dfrac{1}{2}\times h\times BC $
$= \dfrac{1}{2}.|\vec{AB}\times \vec{AC}|$
$\Rightarrow h = \cfrac{|\vec{b}\times \vec{c}|}{|\vec{b}-\vec{c}|}$

Perpendiculars AP, AQ and AR are drawn to the $x-,y-$ and $z-$axes, respectively, from the point $A\left ( 1,-1,2 \right )$. The A.M. of $AP^2,$ $AQ^2$ and $AR^2$ is

  1. $4$

  2. $5$

  3. $3$

  4. $2$


Correct Option: A
Explanation:
$A=(1,-1,2), P=(1,0,0), ,Q=(0,-1,0),R=(0,0,2)$
$AP^2 = [(-1)^2+2^2] = 5$,
$ AQ^2  = [1^2+2^2] = 5$,
$ AR^2 = [(-1)^2+1^2] = 2$
Hence required A.M is $=\cfrac{5+5+2}{3}=4$ 

Perpendicular distance of the point $(3,4,5)$ from the $y$-axis, is

  1. $\sqrt { 34 } $

  2. $\sqrt { 41 } $

  3. $4$

  4. $5$


Correct Option: A
Explanation:

Distance of $\left( \alpha ,\beta ,\gamma  \right) $ from $y$-axis is given by,

$d=\sqrt { { \alpha  }^{ 2 }+{ \gamma  }^{ 2 } } $
$\therefore$ distance $(d)$ of $(3,4,5)$ from $y$-axis is
$d=\sqrt { { 3 }^{ 2 }+{ 5 }^{ 2 } } =\sqrt { 9+25 } =\sqrt { 34 } $

The distance from the point $\displaystyle -\hat i + 2\hat j + 6\hat k$ to the straight line passing through the point with position vector $\displaystyle 2\hat i + 3\hat j - 4\hat k$ and parallel to the vectors $\displaystyle 6\hat i + 3\hat j - 4\hat k$ is

  1. $10$

  2. $7$

  3. $5$

  4. $3$


Correct Option: B
Explanation:
Let $A=(2+6t,3+3t,-4-4t)$ is the point on the line which is least distance from the point $B=(2,3,-4)$. 
Then the vector $BA=(3+6t)i+(2+3t)j+(-10-4t)k$ is perpendicular to $6i+3j-4k$.
$\Rightarrow (3+6t)\times 6+(2+3t)3-(10-4t)4=0$
$\Rightarrow t=-1$
$\Rightarrow A=(-4,0,0)$.
The distance from A to $(-1,2,6)$ is $\sqrt{(-3)^2+2^2+6^2}=7$.

The perpendicular distance of point $(2, -1, 4)$ from the line $\dfrac{x + 3}{10} = \dfrac{y - 2}{-7} = \dfrac{z}{1}$ lies between 

  1. $(2, 3)$

  2. $(3, 4)$

  3. $(4, 5)$

  4. $(1, 2)$


Correct Option: B
Explanation:

Let the foot of perpendicular from $P (2, -1, 4)$ to the given line be $A(10 \lambda - 3, -7 \lambda + 2, \lambda) \overrightarrow{PA} . (10 \hat{i} - 7 \hat{j} + k) = 0$
$\Rightarrow 10 (10 \lambda - 5) - 7 (-7 \lambda + 3) + 1 (\lambda - 4) = 0$
$\Rightarrow 150 \lambda = 75 \Rightarrow  \lambda = \dfrac{1}{2}$
$|\overrightarrow{PA}| = \sqrt{(10 \lambda - 5)^2 + (-7 \lambda + 3)^2 + (\lambda - 4)^2}$
$= \sqrt{0 + \left(\dfrac{1}{2}\right)^2 + \left(\dfrac{7}{2} \right)^2} = \sqrt{\dfrac{50}{4}}$
Which lies in $(3, 4)$

The perpendicular distance of the point $\left ( x,\, y,\, z \right )$ from the x-axis is 

  1. $\sqrt{x^{2}\, +\, y^{2}}$

  2. $\sqrt{y^{2}\, +\, z^{2}}$

  3. $\sqrt{z^{2}\, +\, x^{2}}$

  4. $\sqrt{x^{2}\, +\, y^{2}\, +\, z^{2}}$


Correct Option: B
Explanation:

The given point is $(x,y,z)$

$\therefore$ by distance formula
Distance = $ \sqrt{(x-x)^2+(y-0)^2+(z-0)^2}=\sqrt{y^2+z^2}$

The distance of the point $B$ with position vector $i +2j +3k$ from the line passing through the point $A$ with position vector $4i + 2j + 2k$ and parallel to the vector $2i + 3j + 6k$ is

  1. $\sqrt{10}$

  2. $\sqrt{5}$

  3. $\sqrt{6}$

  4. none of these


Correct Option: A
Explanation:

Equation of the line passing through the point $A\left(4i+2j+2k\right)$ and parallel to $\left(2i+3j+6k\right)$ is
$\overrightarrow { r } = \left(4i+2j+2k\right)+t\left(2i+3j+6k\right)$
any point on the line is of the form $\left(4+2t,2+3t,2+6t\right)$
let $BC$ is perpendicular to the given line, $B\left(i+2j+3k\right)$ and $C\left(4+2t,2+3t,2+6t\right)$
applying perpendicularity condition
$(2t+3)2+(3t)3+(6t-1)6=0$
$\Rightarrow t=0$
$\therefore$ $BA$ is perpendicular to the line
Hence,required distance is $\sqrt{10}$

Perpendicular distance of the point $(3,4,5)$ from the $y$-axis is

  1. $\sqrt { 34 } $

  2. $\sqrt { 41 } $

  3. $4$

  4. $5$


Correct Option: A
Explanation:

Given point is $(3,4,5)$

Distance of $\left( \alpha ,\beta ,\gamma  \right) $, from $y$-axis is given by
$d=\sqrt { { \alpha  }^{ 2 }+{ \gamma  }^{ 2 } } $

$\therefore$ distance $(d)$ of $(3,4,,5)$ from $y$-axis is
$d=\sqrt { { 3 }^{ 2 }+{ 5 }^{ 2 } } =\sqrt { 9+25 } =\sqrt { 34 } $

$A = (0, 1, 2), B=(3, 0, 1), C=(4, 3, 6), D=(2, 3, 2)$ are the rectangular cartesian co-ordinates. Find the perpendicular distance from $A$ to the line $BC$.

  1. $\displaystyle \left ( \dfrac {6}{7} \right )\sqrt{14}$

  2. $\displaystyle \left ( \dfrac {6}{7} \right )\sqrt{18}$

  3. $\displaystyle \left ( \dfrac {4}{7} \right )\sqrt{14}$

  4. $\displaystyle \left ( \dfrac {4}{7} \right )\sqrt{18}$


Correct Option: A

The length of the perpendicular drawn from $(1,2,3)$ to the line $\displaystyle \frac { x-6 }{ 3 } =\frac { y-7 }{ 2 } =\frac { z-7 }{ -2 } $ is

  1. $4$

  2. $5$

  3. $6$

  4. $7$


Correct Option: D
Explanation:

Direction cosines of the given line are  

$\displaystyle \frac { 3 }{ \sqrt { 17 }  } ,\frac { 2 }{ \sqrt { 17 }  } ,\frac { -2 }{ \sqrt { 17 }  } $
$\displaystyle \therefore AM=\left| \left( 6.1 \right) .\frac { 3 }{ \sqrt { 17 }  } +\left( 7-2 \right) .\frac { 2 }{ \sqrt { 17 }  } +\left( 7-3 \right) .\frac { -2 }{ \sqrt { 17 }  }  \right| =17$
$AP=\sqrt { { \left( 16-1 \right)  }^{ 2 }+{ \left( 7-2 \right)  }^{ 2 }+{ \left( 7-3 \right)  }^{ 2 } } $
$=\sqrt { 25+25+16 } =\sqrt { 66 } $
$\therefore$ length of the perpendicular is
$PM=\sqrt { { AP }^{ 2 }-{ AM }^{ 2 } } $
$=\sqrt { 66-17 } =\sqrt { 49 } =7$

The distance between a point $P$ whose position vector is $5\hat{i}+\hat{j}+3\hat{k}$ and the line $\vec{r}=(3\hat{i}+7\hat{j}+\hat{k})+\lambda(\hat{j}+\hat{k})$ is

  1. $3$

  2. $4$

  3. $5$

  4. $6$


Correct Option: D
Explanation:

$\vec{r}= 3\vec{i}+(7+\lambda )\hat{j}+(1+\lambda )\hat{k}$
$(\hat{r}-\hat{a})= -2\hat{i}+(6+\lambda )\hat{j}+(\lambda -2)\hat{k}$
$(\vec{r}-\vec{a})\perp (\hat{j}+\hat{k})$
$(\vec{r}-\vec{a}).(\hat{j}+\hat{k})= 0$
$6+\lambda +\lambda -2= 0$
$\lambda =-2$
$(\vec{r}-\vec{a})= -2\hat{i}+4\hat{j}-4\hat{k}$
$\left | \vec{r}-\vec{a} \right |= 6$

The perpendicular distance of a corner of unit cube from a diagonal not passing through it is

  1. $\sqrt{\dfrac{2}{3}}$

  2. $\dfrac{2}{3}$

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

  4. $

    1$


Correct Option: A
Explanation:

Let P.V. of
$\overline{A}=\overline{0}$
$\overline{B}=\overline{b}$
$\overline{C}=\overline{c}+\overline{b}$
$\overline{D}=\overline{c}$
$\overline{G}=\overline{d}$
$\overline{E}=\overline{c}+\overline{b}+\overline{a}$
$\overline{AE}$ is the main diagonal$=\overline{c}+\overline{b}+\overline{d}$
& $\overline{c}$ be a Corner$=\overline{c}+\overline{b}$
So line equation of $AC=\overline{o}+t(\overline{c}+\overline{b}+\overline{d})$
So, $\bot$ distance $=\dfrac{|(\overline{c}+\overline{b})\times(\overline{c}+\overline{b})+\overline{d}|}{|\overline{c}+\overline{b}+\overline{d}|}$
$=\dfrac{|(\overline{c}+\overline{b})\times\overline{d}|}{\sqrt{3}}$
$=\dfrac{|\overline{c}+\overline{b}||\overline{d}|\sin \theta}{\sqrt{3}}$
$=\dfrac{\sqrt{2}}{3}$

The perpendicular distance from $(4, -3, 2)$ to the line $\displaystyle \dfrac{x-2}{3}=\dfrac{y-3}{-2}=\dfrac{z-5}{6}$ is

  1. $7\sqrt{2}$

  2. $14$

  3. $7$

  4. $49$


Correct Option: C
Explanation:

D.R of line are $3,-2,6$
Now in general the coordinates of any point on line can be represented in the form 
$(3\lambda+2 , -2\lambda + 3 , 6\lambda + 5)$
DR of line perpendicular to the given line $(3\lambda -2 , -2 \lambda + 6 , 6\lambda + 3)$
Now,
 $3(3\lambda -2) -2 (-2\lambda + 6) +6 (6\lambda + 3) = 0$
$\lambda = 0$
Hence, the coordinates are $(2,3,5)$
Distance between points $(2,3,5)$ and $(4,-3,2) = \sqrt {2^2+6^2+3^2} = 7$
Hence, option C is correct.

The distance of the point $A(-2,3,1)$ from the line $BC$ passing through $B(-3,5,2)$ which makes equal angles with the axes is

  1. $\displaystyle \dfrac{2}{\sqrt{3}}$

  2. $\sqrt{\dfrac{14}{3}}$

  3. $\displaystyle \dfrac{16}{\sqrt{3}}$

  4. $\displaystyle \dfrac{5}{\sqrt{3}}$


Correct Option: B
Explanation:

Since $ \alpha = \beta = \gamma $
$\Rightarrow l = m = n = \dfrac{1}{\sqrt{3}}$, where $l,m,n$ are direction cosines of line $PQ$
Let $M$ be a point on the line $PQ$ such that $AM \perp PQ$
So, $PM$  $ =$   Projection of $AP$ on $ PQ$
          

 $ = \mid (-2 + 3)\dfrac{1}{\sqrt{3}} + (3 - 5)\dfrac{1}{\sqrt{3}} +(1 - 2)\dfrac{1}{\sqrt{3}} \mid = \dfrac{2}{\sqrt{3}}$

and $ AP= \sqrt{(-2+3)^2 + (3-5)^2 + (1-2)^2} = \sqrt{6}$
Hence required distance is,
$AM = \sqrt{PQ^2 - QM^2} = \sqrt{\dfrac{14}{3}} $

State the following statement is True or False

Distance of the point $P(x, y, z)$ from the plane $X  Y$ is $\sqrt {x^{2} + y^{2} + z^{2}}$

  1. True

  2. False


Correct Option: B
Explanation:
Co-ordinates of plane $XY$ is $(0,0,z)$, since $Z$ is not included. 
$\therefore $  distance of pt $P(x,y,z)$ from xy plane $(0,0,z)$ is given by
$\sqrt { { (x-0) }^{ 2 }+{ (y-0) }^{ 2 }+{ (z-z) }^{ 2 } } $

$= \sqrt { { x }^{ 2 }+{ y }^{ 2 } } $

$\therefore $ The given statement is FALSE.

The perpendicular distance of$\overrightarrow A $ (1,4,-2) from the segment BC where$\overrightarrow B $  (2,1,-2) and $\overrightarrow C $ (o,-5,1) is 

  1. $\frac{3}{7}\sqrt {26} $

  2. $\frac{6}{7}\sqrt {26} $

  3. $\frac{4}{7}\sqrt {26} $

  4. $\frac{2}{7}\sqrt {26} $


Correct Option: A
Explanation:
We have to find a perpendicular distance $AP$
Now $\vec{AB}=(2, 1, -2)-(1, 4, -2)=(1, -3, 0)$
$\vec{AC}=(0, -5, 1)-(1, 4, -2)=(-1, -9, 3)$
$\vec{AB}\times \vec{AC}\begin{vmatrix} i & j & k \\ 1 & -3 & 0 \\ -1 & -9 & 3 \end{vmatrix}=-9i-3j-12k$
$|\vec{AB}\times \vec{AC}|=\sqrt{(-9)^{2}+(-3)^{2}+(-12)^{2}}=3\sqrt{26}$ units
Area of $\Delta =\dfrac{1}{2}|\vec{AB}\times \vec{AC}|=\dfrac{3}{2}\sqrt{26}$ sq.units
Now $\vec{BC}=(0, -5, 1)-(2, 1, -2)$
$=(-2, -6, 3), |\vec{BC}|=\sqrt{(2)^{2}+(6)^{2}+3^{2}}=7$ units
$=\dfrac{1}{2}\times 7\times AP=\dfrac{3}{2}\sqrt{26}$
$\therefore Ap=\dfrac{3}{7}\sqrt{26}$ units

Find the length of perpendicular from $ P(2, -3, 1)$ to the line $\displaystyle \frac{x- 1}{2} = \frac{y - 3}{3} = \frac{z + 2}{-1}$

  1. $5$

  2. $\displaystyle \sqrt{\dfrac{531}{14}}$

  3. $\sqrt{50}$

  4. $\sqrt{\dfrac{221}{3}}$


Correct Option: B
Explanation:

Let take a point on line $(2\lambda +1,3\lambda +3,-\lambda -2)$


Direction ratio's of line which is  perpendicular to given line, 

$(2\lambda +1-2,3\lambda +3+3,-\lambda -2-1)$

$(2\lambda -1,3\lambda +6,-\lambda -3)$

And the direction ratio's of given line are $2,3,-1$.

These two lines are perpendicular, so

$(2\lambda -1)\cdot 2+(3\lambda +6)\cdot 3+(-\lambda -3)+(-1)=0$


$\lambda=\dfrac{-19}{14}$

So point is $\left (\dfrac{-24}{14},\dfrac{-15}{14},\dfrac{-9}{14}\right)$

So distance between $\left (\dfrac{-24}{14},\dfrac{-15}{14},\dfrac{-9}{14}\right) $ and $(1,3,-2)$ is $\sqrt{\dfrac{531}{14}}$...................(by distance formula) 

A line is drawn from $P(x _1 , y _1)$ in the direction $\theta$ with the X - axis, to meet $ax + by + c = 0$ at $Q$. Then length $PQ$ is equal to :

  1. $\dfrac{|ax _1 + by _1 + c|}{\sqrt{(a^2 + b^2)}}$

  2. $\left|\dfrac{ax _1 + by _1 + c}{a \, cos \theta + b \, sin \theta} \right|$

  3. $\dfrac{bx _1 + ay _1 + c}{a cos \theta + b sin \theta}$

  4. $ - \dfrac{ax _1 + by _1 + c}{a sin \theta + b cos \theta}$


Correct Option: B
Explanation:
Equation of a line drawn through a point $P\left( { x } _{ 1 }{ y } _{ 1 } \right) $ at an angle $\theta $ with the $x-axis$
$\dfrac { x-{ x } _{ 1 } }{ \cos\theta  } =\dfrac { y-{ y } _{ 1 } }{ \sin\theta  } \quad \longrightarrow \left( 1 \right) $
$Q$ is a point the above line and also lies on the line $ax+by+cz=0$
Say $\left| PQ \right| =r$ and the coordinates of $Q$ are $\left( h,k \right) $
Then,
$h={ x } _{ 1 }+r\cos\theta $
$k={ y } _{ 1 }+r\sin\theta $
$\because$   $Q$ lies on $ax+by+cz=0$
$\therefore$   $ah+bk+c=0$
$\Rightarrow a\left( { x } _{ 1 }+r\cos\theta  \right) +b\left( { y } _{ 1 }+r\sin\theta  \right) +c=0$
$\Rightarrow { ax } _{ 1 }+{ by } _{ 1 }+c+r\left( a\cos\theta +b\sin\theta  \right) =0$
$\Rightarrow \quad r=\dfrac { -\left( { ax } _{ 1 }+{ by } _{ 1 }+c \right)  }{ a\cos\theta +b\sin\theta  } $
$\because$   $'r'$ is the magnitude of length of line segment $PQ$, it cannot be negative.
So, $r=\left| \dfrac { { ax } _{ 1 }+{ by } _{ 1 }+c }{ a\cos\theta +b\sin\theta  }  \right| $

The $\perp $ distance of a corner of a unit cube on a diagonal not passing through is 

  1. $\displaystyle \frac{\sqrt{6}}{3}$

  2. $3\sqrt{3}$

  3. $2\sqrt{3}$

  4. None of these


Correct Option: A
Explanation:
Let the edges Of unit cube are OA along z axis,OB along x axis and OC along y axis.
Let CM be the perpendicular from corner C on diagonal OP where point P is (1,1,1)
OP = $ \vec i+ \vec j+ \vec k$

Unit vector in the direction of OP is  = $\dfrac {\vec i+ \vec j+ \vec k}{\sqrt 3}$
OM= projection of OC on OP
OM=  OC . (unit  vector of OP)

OM=$\vec j \dfrac {((\vec i+\vec j+\vec k)}{\sqrt3}$=$1 \sqrt 3$

Now $CM^2=OC^2−OM^2$

$CM^2$=$1-\dfrac {1} {3}$ = $\dfrac {2} {3}$

So CM = $\dfrac {\sqrt 2}{\sqrt 3}$ = $\dfrac {\sqrt 6}{ 3}$


The perpendicular distance of the point $P(1,2,3)$ from the straight line passing through the point $A(-1,4,7)$ and $B(2,8,7)$

  1. $\displaystyle \frac{\sqrt{149}}{25}$

  2. $\displaystyle \frac{149}{25}$

  3. $\displaystyle \frac{2\sqrt{149}}{25}$

  4. $\displaystyle \frac{2\sqrt{149}}{5}$


Correct Option: D
Explanation:

The drs of line joining points $A(-1,4,7)$ and $B(2,8,7)$ are $3,4,0$

The equation of line $AB$ is $\frac{x+1}{3}=\frac{y-4}{4}=\frac{z-7}{0}$
So the point on line $AB$ will look like $C(3t-1,4t+4,7)$
Assume that $CP$ is perpendicular to $AB$
So we get $(3t-2)3+(4t+2)4=0$
$\Rightarrow t=-\frac{2}{25}$
So the point $C$ is $(-\frac{31}{25}\frac{92}{25},7)$
The length of $CP$ is $\sqrt { { (\frac { 56 }{ 25 } ) }^{ 2 }+{ (\frac { 42 }{ 25 } ) }^{ 2 }+{ 7 }^{ 2 } } =\frac{2\sqrt{149}}{5}$
Therefore the correct option is $D$

The distance from the point $(1,6,3)$ to the line $\bar{r}=(\hat{j}+2\hat{k})+\lambda(\hat{i}+2\hat{j}+3\hat{k})$ is

  1. $\sqrt{13}$

  2. $13$

  3. $2\sqrt{13}$

  4. None of these


Correct Option: A
Explanation:

Using fact the $\perp$ distance from $(\alpha,\beta,\gamma)$ in the line

$\displaystyle \dfrac{x-x _{1}}{1}=\dfrac{y-y _{1}}{m}=\dfrac{z-z _{1}}{n}$ is given by 

$\sqrt{(\alpha-x _{1})^{2}+(\beta-y _{1})^{2}+(\gamma-z _{1})^{2}}$

$\sqrt{-[l(\alpha-x _{1})+m(\beta-y _{1})+n(\gamma-z _{1})]^{2}}$

Now $(\alpha,\beta,\gamma)=(1,6,3),(x _{1},y _{1}.z _{1})=0,1,2,l,m,n=\dfrac{1}{\sqrt{14}},\dfrac{1}{\sqrt{14}},\dfrac{1}{\sqrt{14}}$

$\therefore$ Required distance

$\displaystyle =\sqrt{(1-0)^{2}+(6-1)^{2}+(3-2)^{2}-\left[\dfrac{1}{\sqrt{14}}(1+2(5)+3(1)\right]^{2}}=\sqrt{27-14}=\sqrt{13}$

If $\vec {a},\vec {b},\vec {c}$ are position vectors of the non-collinear points $A, B, C$ respectively, then the shortest distance of $A$ from $BC$ is

  1. $\vec {a}.(\vec {b}-\vec {c})$

  2. $|\displaystyle \vec {b}-\vec {a}|-\left(\dfrac{(\vec {a}-\vec {b}).(\vec {c}-\vec {b})}{|\vec {c}-\vec {b}|}\right)^{2}$

  3. $|\vec {b}-\vec {a}|$

  4. $\displaystyle \sqrt {(|\vec {b}-\vec {a}|)^2-\left(\dfrac{(\vec {b}-\vec {a}).(\vec {c}-\vec {b})}{|\vec {c}-\vec {b}|}\right)^{2}}$


Correct Option: D
Explanation:

We know that shortest distance is $\bot$ distance
$=\dfrac{|(\overline{b}-\overline{a})\times(\overline{c}-\overline{b})|}{|(\overline{c}-\overline{b})|}$


$=\dfrac{1}{|\overline{c}-\overline{b}|}\sqrt{|\overline{b}-\overline{a}|^2|\overline{c}-\overline{b}|^2-((\overline{b}-\overline{a})\cdot(\overline{c}-\overline{b}))^2}$

$=\sqrt{|\overline{b}-\overline{a}|^2-\left ( \dfrac{(\overline{b}-\overline{a})\cdot(\overline{c}-\overline{b})}{|\overline{c}-\overline{b}|} \right )^2}$

- Hide questions