Each interior angle of a regular decagon ($n=10$) measures:

Each interior angle of a regular decagon ($n=10$) measures:
  1. $135^{\circ}$
  2. $140^{\circ}$
  3. $144^{\circ}$
  4. $150^{\circ}$

Solution

Each interior angle $= \dfrac{(10-2) \times 180^{\circ}}{10} = \dfrac{1440^{\circ}}{10} = 144^{\circ}$.

Asked in: IMO

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