Interior Angle of Polygon in terms of Exterior Angle

Last updated at August 4, 2026 by

Let us consider a triangle ∆ ABC

 

Let ∠ 1 be the exterior angle

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Since BAD is a line

  ∠ A + ∠1 = 180°      (Linear Pair)

  ∠ 1 = 180° − ∠ A

 

So, in a polygon

  Interior angle + Exterior angle = 180°

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