Remote Interior and Exterior Angles in a Triangle
The measurement of an exterior angle of a triangle equals the sum of the remote interior angles.
In the figure, the remote interior angles have measures of 80° and 55°. The sum is 80° + 55° = 135°.
Applying the statement described above, the measurement of angle 4 is:
m∠4 = 80° + 55° = 135°.
m∠4 = 135°