Angles of a Triangle Add to 180 degrees

Angles of a Triangle Add to 180 degrees is a Grade 8 geometry discovery activity that makes the triangle angle-sum relationship visible. Students draw and cut out different triangles, remove the three corners, and line the angles up to form a straight angle. Repeating the experiment with different triangle shapes helps them see that the 180° total is not tied to one special example.

Use it as a whole-class hands-on investigation before or during formal work with missing triangle angles. Ask students what stays the same when the triangle changes from acute to obtuse or equiangular. Generate teacher-ready lesson support for this activity with a free account. No credit card required; 3 lesson generations for life.