Question

If a focal chord of parabola y² = ax is 2x – y – 8 = 0 then the equation of directrix is:

• A. x + 4 = 0
• B. x – 4 = 0
• C. y – 4 = 0
• D. y + 4 = 0

Answer 1

Answer: (A)

x + 4 = 0

Answer 2

Focus $\left( \frac{a}{4},0 \right)$

Put in 2x – y – 8 = 0

̃ 2 × – 0 = 8

̃ a = 16

parabola y² = 16x

Directrix x = – 4