Question 33

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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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