Geometry and Measurement — Triangle

About this lesson

This unit teaches properties of triangles in geometry. It covers the sum of interior angles of a triangle (180°), the concept of an exterior angle and its relationship to the two non-adjacent interior angles, and the triangle inequality (the sum of any two sides is greater than the third side). Students learn to find unknown angles and side lengths using these rules, and to determine whether a set of side lengths can form a triangle. The unit includes practical activities with drawing triangles using a compass and ruler, and real-life applications such as construction, boat sails, and a car barrier. By the end, students should be able to apply these rules to solve problems involving angles and side lengths, and to verify solutions.