Question 12

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Jambmaths question: 

$\begin{align}  & \text{If }x-4\text{ is a factor of }{{x}^{2}}-x-k,\text{ then }k\text{ is } \\ & \text{(A) 4  (B) 12 (C) 20  (D) 2} \\\end{align}$

Jamb Maths Solution: 

$\begin{align}  & \text{Let }f(x)={{x}^{2}}-x-k,\text{ } \\ & \text{if }x-4\text{ is a factor of }f(x)\text{ then }f(4)=0 \\ & {{4}^{2}}-4-k=0 \\ & 16-4-k=0 \\ & k=12 \\\end{align}$

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