Related Topics: More Geometry Lessons
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 explains the Exterior Angle Theorem and how it can be used the find the angles in a triangle.
The following video shows how to use the Exterior Angle Theorem to solve problems involving angles in a triangle.
This video provides a two column proof of the exterior angles theorem
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