Defining Exterior Angles of a Triangle
Defining Exterior Angles of a Triangle is a Grade 7 math skill in Big Ideas Math Advanced 2, Chapter 3: Angles and Triangles, where students learn that an exterior angle of a triangle is formed by extending one side of the triangle, and apply the Exterior Angle Theorem — that an exterior angle equals the sum of the two non-adjacent interior angles — to find unknown angle measures.
Key Concepts
An exterior angle of a triangle is formed when one side of the triangle is extended beyond a vertex. The exterior angle and its adjacent interior angle are supplementary, meaning they sum to $180°$.
Common Questions
What is an exterior angle of a triangle?
An exterior angle is formed when one side of a triangle is extended beyond a vertex. It is supplementary to the adjacent interior angle (together they form a straight line).
What does the Exterior Angle Theorem state?
The Exterior Angle Theorem states that the measure of an exterior angle of a triangle equals the sum of the two non-adjacent (remote) interior angles.
How do you use the Exterior Angle Theorem to find missing angles?
If you know the exterior angle and one of the remote interior angles, subtract to find the other. If you know both remote interior angles, add them to find the exterior angle.
What is Big Ideas Math Advanced 2 Chapter 3 about?
Chapter 3 covers Angles and Triangles, including angle-sum theorems, the Exterior Angle Theorem, and problem solving with interior and exterior angles.