In this Grade 7 lesson from Big Ideas Math Advanced 2, students learn that the sum of the interior angle measures of a triangle is 180° and apply the Exterior Angle Theorem, which states that an exterior angle equals the sum of the two nonadjacent interior angles. Students practice finding unknown angle measures by setting up and solving algebraic equations using these relationships. The lesson builds understanding of interior and exterior angles of polygons within the broader study of angles and triangles.
Section 1
Defining Exterior Angles of a Triangle
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 .
Section 2
Triangle Angle-Sum Theorem
The sum of the interior angles in any triangle is .
Section 3
Exterior Angle Theorem
An exterior angle is formed when one side of a triangle is extended outward. It forms a linear pair (summing to 180°) with its adjacent interior angle.
The Exterior Angle Theorem states that the measure of an exterior angle equals the sum of the two non-adjacent (remote) interior angles:
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Section 1
Defining Exterior Angles of a Triangle
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 .
Section 2
Triangle Angle-Sum Theorem
The sum of the interior angles in any triangle is .
Section 3
Exterior Angle Theorem
An exterior angle is formed when one side of a triangle is extended outward. It forms a linear pair (summing to 180°) with its adjacent interior angle.
The Exterior Angle Theorem states that the measure of an exterior angle equals the sum of the two non-adjacent (remote) interior angles:
Book overview
Jump across lessons in the current chapter without opening the full course modal.
Continue this chapter