Question 49

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waecmaths question: 

Simplify $\frac{20}{5\sqrt{28}-2\sqrt{63}}$

Option A: 

$\frac{5\sqrt{7}}{7}$

Option B: 

$\frac{5\sqrt{5}}{7}$

Option C: 

$\frac{7\sqrt{5}}{7}$

Option D: 

$\frac{7\sqrt{7}}{5}$

waecmaths solution: 

$\begin{align}  & \frac{20}{5\sqrt{28}-2\sqrt{63}}=\frac{20}{\sqrt{4\times 7}-\sqrt{9\times 7}} \\ & \frac{20}{5\sqrt{28}-2\sqrt{63}}=\frac{20}{10\sqrt{7}-6\sqrt{7}} \\ & \frac{20}{5\sqrt{28}-2\sqrt{63}}=\frac{20}{4\sqrt{7}}=\frac{5}{\sqrt{7}} \\ & \frac{20}{5\sqrt{28}-2\sqrt{63}}=\frac{5}{\sqrt{7}}\times \frac{\sqrt{7}}{\sqrt{7}}=\frac{5\sqrt{7}}{7} \\\end{align}$

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