Correct Answer: Option C

Explanation

y = 2kx² + x + 1
Gradient function dy/dx = 4kx + 1
at dy/dx = 9, => 9 = 4kx + 1
=> 8 = 4kx, and k = 8/4x.

At x = 1, k = 8/4 = 2

There is an explanation video available below.

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