Find Triangle Angles: Isosceles Triangle with 76° and Parallel Lines

Question

Lines a and b are parallel.

The triangle ABC is isosceles.

What are the sizes of its angles?

00:00 Prove that the triangle is isosceles and find its angles

00:06 Vertical angles are equal

00:15 Adjacent angles sum to 180 degrees

00:18 Therefore subtract the known angles from 180 to find the angle

00:31 Corresponding angles between parallel lines are equal

00:41 Adjacent angles sum to 180 degrees

00:45 Therefore subtract the known angles from 180 to find the angle

00:50 The base angles of triangle ABC are equal

00:56 In an isosceles triangle, the base angles are equal

01:01 The sum of angles in a triangle equals 180 degrees

01:05 Therefore subtract the known angles from 180 to find the angle

01:14 And this is the solution to the problem

41, 41, 98