waecmaths question:
What is the diameter of a circle of area 77cm2 (take $\pi =\tfrac{22}{7}$ )
Option A:
$\tfrac{\sqrt{2}}{7}cm$
Option B:
$3\tfrac{1}{2}cm$
Option C:
7cm
Option D:
$7\sqrt{2}cm$
waecmaths solution:
$\begin{align} & A=\frac{\pi {{d}^{2}}}{4} \\ & 77c{{m}^{2}}=\frac{22{{d}^{2}}}{7\times 4} \\ & {{d}^{2}}=\frac{77\times 7\times 4}{22}=49\times 2 \\ & d=\sqrt{49\times 2}=7\sqrt{2}cm \\\end{align}$
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