Practice Triangle Angle Sum in Math
Use these practice problems to test your method after reviewing the concept explanation and worked examples.
Quick Recap
The three interior angles of any triangle always sum to exactly 180°, so knowing two angles determines the third.
Tear off the three corners of any paper triangle and line them up—they always form a straight line (180°). No matter how pointy or flat the triangle is, the angles always add up the same way, like three puzzle pieces that always complete a half-turn.
Example 1
easyA triangle has angles 55° and 72°. Find the third angle.
Example 2
mediumIn an isosceles triangle, the vertex angle is 40°. Find the two base angles.
Example 3
easyCan a triangle have angles of 90°, 91°, and 1°? Justify your answer.
Example 4
hardIn \triangle ABC, \angle A = 2x + 10°, \angle B = 3x - 5°, \angle C = x + 15°. Find all three angles.