CK-12 Geometry-Concepts

http://www.ck12.org Chapter 4. Triangles and Congruence

4.2 Exterior Angles Theorems

Here you’ll learn what an exterior angle is as well as two theorems involving exterior angles: that the sum of the
exterior angles is always 360◦and that in a triangle, an exterior angle is equal to the sum of its remote interior angles.

What if you knew that two of the exterior angles of a triangle measured 130◦? How could you find the measure of
the third exterior angle? After completing this Concept, you’ll be able to apply the Exterior Angle Sum Theorem to
solve problems like this one.

Watch This

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CK-12 Foundation: Chapter4ExteriorAnglesTheoremsA

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James Sousa: Introduction to the Exterior Angles of a Triangle

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James Sousa: Proof that the Sum of the Exterior Angles of a Triangle is 360 Degrees

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James Sousa: Proof of the Exterior Angles Theorem