What is the relationship between one interior angle and its exterior angle?

1 Answer
Aug 18, 2016

Sum of an interior angle of a triangle and its exterior angle is #180^o#, so these two angles are supplementary.

Explanation:

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Interior angle is formed by two sides of a polygon.
The corresponding exterior angle is formed by one of these sides and continuation of another (see the drawing.)

That makes these two angles adjacent to each other and together forming a straight angle of #180^o# degree.

Therefore, these two angles are supplementary and, added up, make #180^o#.