Let P be the parabola, whose focus is (-2, 1) and directrix is 2x + y + 2 = 0. Then the sum of the ordinates of the points on P, whose abscissa is -2, is
- 52
- 32
- 34
- 14
Answer
(2) 32
Solution
For a point (x, y) on P: distance from focus = distance from directrix
(x + 2)2 + (y - 1)2 = (2x + y + 2)25
Put x = -2:
(y - 1)2 = (y - 2)25
5y2 - 10y + 5 = y2 - 4y + 4
4y2 - 6y + 1 = 0 (real roots, D = 36 − 16 = 20 > 0)
sum of ordinates = 64 = 32
Answer: (2)