Question 20

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waecmaths question: 

What must be added to ${{x}^{2}}-3x$ to make it a perfect square?

Option A: 

$\tfrac{9}{4}$

Option B: 

$\tfrac{9}{2}$

Option C: 

6

Option D: 

9

waecmaths solution: 

$\begin{align}  & {{x}^{2}}-3x \\ & \text{For perfect square }{{b}^{2}}=4ac \\ & \therefore {{x}^{2}}-3x+c \\ & a=1,\text{ }b=-3,\text{ }c=k \\ & {{(-3)}^{2}}=4(1)(k) \\ & 9=4k \\ & k=\tfrac{9}{4} \\\end{align}$

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