Jambmaths question:
If the gradient of the curve $y=2k{{x}^{2}}+x+1$ at x = 1 is 9. Find k
Option A:
4
Option B:
3
Option C:
2
Option D:
1
Jamb Maths Solution:
$\begin{align} & y=2k{{x}^{2}}+x+1 \\ & \frac{dy}{dx}=4kx+1 \\ & at\text{ }x=1,\text{ }\frac{dy}{dx}=9 \\ & 9=4k(1)+1 \\ & 8=4k \\ & k=2 \\\end{align}$
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