JEE-Mains 2015 (19/30)

Geometry Level 3

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

circle of radius 2 \sqrt{2} . straight line parallel to y-axis. circle of radius 3 \sqrt{3} . straight line parallel to x-axis.

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1 solution

Pushpa Sharma
May 19, 2017

The given line is a family of lines passing through the point of intersection of 2 x 3 y + 4 = 0 2x-3y+4=0 and x 2 y + 3 = 0 x-2y+3=0 i.e. P ( 1 , 2 ) P (1,2) . Let the co-ordinates of the image be ( h , k ) (h,k) . Distance of P P from ( 2 , 3 ) (2,3) is 2 \sqrt 2 . So ( h , k ) (h,k) will also be at a distance of 2 \sqrt 2 from P P . Therefore the locus is: ( h 1 ) 2 + ( k 2 ) 2 = 2 (h-1)^2 + (k-2)^2 = 2 . Hence (B).

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