An exterior angle of a triangle is formed by any side of a triangle and the extension of its adjacent side.
The Exterior Angle Theorem states that
An exterior angle of a triangle is equal to the sum of the two opposite interior angles.
Find the values of x and y in the following triangle.
x + 50° = 92° (sum of opposite interior angles = exterior angle)
x = 92° – 50° = 42°
y + 92° = 180° (interior angle + adjacent exterior angle = 180°.)
y = 180° – 92° = 88°
The following video gives a definition of exterior angles and shows how to find the unknown exterior angle of a triangle
This video provides a two column proof of the sum of the exterior angles of a triangle is 360 degree.
Rotate to landscape screen format on a mobile phone or small tablet to use the Mathway widget, a free math problem solver that answers your questions with step-by-step explanations.