Exterior Angle Theorem

An exterior angle of a triangle is formed when any side is extended outwards.

Exterior Angle Theorem - An exterior angle of a triangle is equal to the sum of the two opposite interior angles.

Example :

Example :

Find the values of x and y in the following triangle.

Solution:

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 explains the Exterior Angle Theorem and how it can be used the find the angles in a triangle.

The follwing video shows how to use the Exterior Angle Theorem to solve problems involving angles in a triangle.

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