Table of Contents
Table of Contents
- Exterior Angle of a Triangle
- Interior Adjacent and Interior Opposite Angles
- Exterior Angle Property of a Triangle
- Summary
- What’s Next?
In the previous segment, we learnt about Altitudes of a triangle. In this segment, we will learn about Exterior angle of a triangle and its property.
What is an Exterior angle of a triangle?
An Exterior angle of a triangle is an angle formed by one side of the triangle and the
extension of an adjacent side of the triangle.
For example,
consider △ABC. Extending side BC to point D gives a straight line BD.
The angle formed by line BD and the side AC lies in the exterior of the triangle. Hence, ∠ACD is called the exterior angle of the triangle.
Exterior angle of a triangle
What are Interior adjacent and Interior opposite angles?
The angles of a triangle are its interior angles.
The interior angle that is adjacent to the exterior angle is the Interior adjacent angle. The remaining two interior angles which are not adjacent to the exterior angle are called Interior opposite angles.
So, for the exterior ∠ACD, the interior angle ∠ACB is its interior adjacent angle and the interior angles ∠ABC and ∠BAC are the interior opposite angles.
