Let (x,y) be any point on the parabola y2=4x. Let P be the point that divides the line segment from (0,0) to (x,y) in the ratio 1:3. Then the locus of P is
(A)x2=y
(B)y2=2x
(C)y2=x✓ Correct
(D)x2=2y
Answer: (C)
Solution
Let P=(h,k) divide the segment from (0,0) to (x,y) in ratio 1:3.
Using section formula:
h=1+31⋅x+3⋅0=4x,k=1+31⋅y+3⋅0=4y
So x=4h and y=4k.
Since (x,y) lies on y2=4x:
(4k)2=4(4h)
16k2=16h
k2=h
Replacing h with x and k with y, the locus is y2=x.
JEE Advanced · 2011 · 10 Apr 2011 · Paper 2 · Single correct option