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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