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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