Ontario Curriculum Expectation:
6.E2.3 use the properties of supplementary angles, complementary angles, opposite angles, and interior and exterior angles to solve for unknown angle measures.
Interior angles are the three angles inside a triangle.
The sum of the three interior angles is always 180º.
Finding the Unknown Angle
180° = a + b + c
180° = 70º + 85º + c
180° = 155º + c
c = 180° − 155º
c = 25º