Question 35

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Jambmaths question: 

The expression of $a{{x}^{2}}+bx+c$equals 5 at x =1. If its derivative is 2x + 1, what are the value of a, b,  respectively.

Option A: 

1, 3, 1

Option B: 

1,1, 3

Option C: 

2, 1, 1

Option D: 

1, 2, 1

Jamb Maths Solution: 

$\begin{align}  & \frac{dy}{dx}=2x+1 \\ & y=\int{(2x+1)dx} \\ & y={{x}^{2}}+x+c \\ & \text{At }x=1,y=5 \\ & 5={{1}^{2}}+1+c \\ & c=3 \\ & y={{x}^{2}}+x+3 \\ & a=1,\text{ }b=1,\text{ }c=3 \\\end{align}$

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