JEE Main2015MathematicsParabolaActual
If P Q be a double ordinate of the parabola, y 2 = - 4 x , where P lies in the second quadrant. If R divides P Q in the ratio 2 : 1 , then the locus of R is:
Options
- A3 y 2 = - 2 x
- B9 y 2 = 4 x
- C9 y 2 = - 4 x
- D3 y 2 = 2 x
Correct answer
C. 9 y 2 = - 4 x
Step-by-step solution
Let P - t 2 , 2 t   &   Q - t 2 , - 2 t R divides in the ratio 2 : 1 - 2 t 2 - t 2 2 + 1 , - 4 t + 2 t 2 + 1 - t 2 , 2 3 t x = - t 2 y = - 2 3 t ∴   9 y 2 = 4 t 2 ⇒ 9 y 2 = - 4 x