Interior and exterior angles of polygons

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Learn it Interior angles of an n-sided polygon add to $(n - 2) \times 180°$. Exterior angles of any polygon add to $360°$. In a regular polygon each exterior angle is $\frac{360°}{n}$, and interior + exterior = $180°$.

Example: Each interior angle of a regular polygon is $150°$. How many sides?

Exterior angle: $180° - 150° = 30°$.
$n = 360 \div 30 = 12$ sides.

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