Question

If vertex of a parabola is (2, –1) and the equation of its directrix is 4x – 3y = 21, then the length of its latus rectum is :

• A. 2
• B. 8
• C. 12
• D. 16

Answer 1

Answer: (B)

8

Answer 2

The correct answer is (B) : 8
Vertex of Parabola : (2, –1)
and directrix : 4x – 3y = 21
Distance of vertex from the directrix
$a=|\frac{8+3−21}{\sqrt25}|=2$
∴ length of latus rectum
= 4a
= 4 × 2= 8