Question

The equation of the directrix of the parabola x² + 8y - 2x = 7 is

(a) y = 3 

(b) y = -3

(c) y = 2 

(d) y = 0

Answer 1

Correct option (a) y = 3  

Explanation:

Given, equation of parabola is x² + 8y - 2x = 7 

⇒ x² - 2x + 8y - 7 = 0

⇒ x² - 2x + 1 + 8y - 7 -1 = 0 

⇒ (x -1)² + 8y = 8

⇒ (x - 1)² = -8(y -1) 

⇒ (x - 1)² = -4.2(y - 1)

Here, a = 2 .

∴ Equation of directrix is y - 1 = 2 i.e., y = 3 .