Lesson 4.2: Angles of Triangles

Key Concepts: Angles of Triangles

Triangle Angle Sum Theorem

The sum of the measures of the interior angles of a Triangle is 180°.

m∠A + m∠B + m∠C = 180°

Exterior Angle Theorem

The measure of an exterior Angle of a Triangle equals the sum of the two non-adjacent interior angles (remote interior angles).

Corollaries

  • The acute angles of a right Triangle are complementary (sum to 90°).
  • A Triangle can have at most one right Angle or obtuse Angle.
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