Question

If x + 2y + 3 = 0 is a tangent to the parabola y² = kx then value of k is

• A. 3
• B. –3
• C. 12
• D. –12

Answer 1

Answer: (A)

3

Answer 2

x + 2y + 3 = 0

y = –$\frac{1}{2}$x – $\frac{3}{2}$; y² = kx

Common tangent

c = a/m

–$\frac{3}{2}$ = $\frac{k/4}{- 1/2}$

Ž $\frac{k}{4}$ = +$\frac{3}{4}$ Ž k = 3