Area of regular polygons (apothem)

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Learn it Any regular polygon splits into identical triangles from its centre. The apothem (centre to the middle of a side) is their height, so $A = \frac{1}{2} \times \text{perimeter} \times \text{apothem}$.

Example: A regular pentagon has side 10 cm and apothem 6.9 cm.

Perimeter: $5 \times 10 = 50$ cm.
$A = \frac{1}{2} \times 50 \times 6.9$.
$A = 172.5$ cm².

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