1.

If 2x + y + k = 0 is a normal to the parabola y2 = − 8x, then the value of k is(A)  12(B)   24(C)  − 12(D)  − 24

Answer»

Correct option (B)  24

Explanation :

Suppose 2x + y + k = 0 is normal at (-2t2, -4t). However, the normal at (-2t2, -4t) is

tx + y = -4t - 2t3

⇒ tx + y + 4t + 2t3 = 0

Therefore

t/2 = 1/1 = 4t + 2t3/k

⇒ t = 2 and k = 24



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