If the gradient of the curve y = 2kx2 + x + 1 at x = 1 is 9, find k.
-
A.
4 -
B.
3 -
C.
2 -
D.
1
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