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Exterior Angle

Definition Of Exterior Angle

An Exterior Angle of a polygon is the angle formed when one side is extended beyond its adjacent sides.

When two lines are cut by a third line (transversal), then the angles formed outside the lines are called Exterior Angle.

More About Exterior Angle

The number of exterior angles in a polygon = The number of sides of the polygon
The exterior angle is supplemental to the adjoining interior angle.
Thesum of the measures of exterior angles of a convex polygon is 360°.
Measure of the exterior angle of a triangle is equal to the sum of its two remote angles.

Video Examples: Angles in polygons- exterior angles
 

Example of Exterior Angle

 example of  Exterior Angle

∠1, ∠2, and ∠3 are the exterior angles.

                       example of  Exterior Angle
∠4, ∠5, ∠6, and ∠ 7 are the exterior angles.

Solved Example on Exterior Angle

Ques: Identify the pair of exterior angles in the figure.

Choices:

A. 1 and 2
B. 2 and 4
C. 1 and 3
D. 3 and 4
Correct Answer: C

Solution:

Step 1: An Exterior Angle of a polygon is the angle formed when one side is extended to its adjacent sides. 
Step 2: From the figure, the angles 1 and 3 are exterior because one side is extended to its adjacent sides.
Step 3: So, 1 and 3 is a pair of exterior angles.