Tag: reflection w.r.t a line

Questions Related to reflection w.r.t a line

The new equation of the curve $4(x-2y+1)^{2}+9(2x+y+2)^{2}=25$ if the lines $2x+y+2=0$ and $x-2y+1=0$ are taken as the new $x$ and $y$ axes respectively is

  1. $4X^{2}+9Y^{2}=5$

  2. $4X^{2}+9Y^{2}=25$

  3. $4X^{2}+9Y^{2}=7$

  4. $4X^{2}-9Y^{2}=7$


Correct Option: A

The coordinates axes are rotated about the origin $O$ in the counter clockwise direction through an angle of $\dfrac{\pi}{6}$. If $a$ and $b$ are intercepts made on the new axes by a straight line whose equation referred to old the axes is $x+y=1$, then the value of $\displaystyle \frac{1}{a^{2}}+\displaystyle \frac{1}{b^{2}}$ is equal to

  1. $1$

  2. $2$

  3. $4$

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


Correct Option: B
Explanation:

Given equation is $x+y=1$
We know that 
$\displaystyle x=X\cos\theta-Y\sin\theta$
$y=X\sin\theta+Y\cos\theta$
$\Rightarrow (\cos\theta+\sin\theta)X+(\cos\theta-\sin\theta)Y=1$  
$\displaystyle \Rightarrow \frac{(\sqrt{3}+1)}{2}X+ \frac{(1-\sqrt{3})}{2}Y=1$       .....(i)
According to problem, we have

$\displaystyle\frac{X}{a}+\frac{Y}{b}=1$ .....(ii)
$\displaystyle\Rightarrow \frac { 1 }{ a } =\frac { (\sqrt { 3 } +1) }{ 2 } $
$\Rightarrow \displaystyle \frac { 1 }{ b } =\frac { (1-\sqrt { 3 } ) }{ 2 } $
So, $\displaystyle \frac { 1 }{ { a }^{ 2 } } +\frac { 1 }{ { b }^{ 2 } } =2$

The reflection of the plane $x+y+z-3=0$ in the plane $2x+3y+4z-6=0$

  1. $1/6$

  2. $\sqrt6$

  3. $4x+3y-2z+15=0$

  4. None of these


Correct Option: B

Reflection of the line $\dfrac{x-1}{-1}=\dfrac{y-2}{3}=\dfrac{z-4}{1}$ in the plane $x+y+z=7$ is:

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

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

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

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


Correct Option: B

The image of the line $x-y-1=0$ in the line $2x-3y+1=0$ is

  1. $7x-17y+23=0$

  2. $17x-7y+23=0$

  3. $7x+17y+23=0$

  4. $ 17x+7y+23=0$


Correct Option: A

The image of the point A$(1,2)$ by the line mirror y=x and the image of B by the line mirror $y=0$ is the point $\left(\alpha, \beta \right)$, then :

  1. $\alpha =1,\beta =-2$

  2. $\alpha =0,\beta =0$

  3. $\alpha =2,\beta =-1$

  4. None of these


Correct Option: C

A ray of light travelling along the line $x+\sqrt{3}y=5$ is incident on the $x-axis$ and after refraction it enters the other side of the $x-axis$ by turning $\dfrac{\pi}{6}$ away from the $x-axis$. The equation of the line along which the refracted ray travels is

  1. $x+\sqrt{3}y-5\sqrt{3}=0$

  2. $x-\sqrt{3}y-5\sqrt{3}=0$

  3. $\sqrt{3}x+y-5\sqrt{3}=0$

  4. $\sqrt{3}-y-5\sqrt{3}=0$


Correct Option: A

If $B$ is reflection of $A(a,5)$ about line $4x-3y=0$, then area of triangle $ABC$ is equal to

  1. $\dfrac{253}{50}$

  2. $\dfrac{506}{25}$

  3. $\dfrac{253}{25}$

  4. $\dfrac{506}{50}$


Correct Option: A

Locus of the image of the point (2, 3) in the line (2x - 3y + 4) + k(x - 2y + 3) = 0, k $\in $ R, is a 

  1. straight line parallel to x-axis

  2. straight line parallel to y-axis

  3. Circle of radius $\sqrt { 2 } $

  4. circle of radius 3


Correct Option: A

The distance of the image of a point (or an object) from the line of symmetry (mirror) is  ----- as that of the point (object )from the line (mirror).

  1. same 

  2. double

  3. triple

  4. none


Correct Option: A
Explanation:
To make the above statement true, the word to be placed in the blank is : “same”
So, the true statement becomes :
The distance of the image of a point (or an object) from the line of symmetry (mirror) is same as that of the point (object) from the line (mirror).
Hence, option A is the correct answer.