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
Verified Correct Answer: C.
Step-by-Step Mathematical Solution
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
Source: Myschool Past Questions Archive (Record #2126)