Sums of Triangle Interior Angles
Follow the steps below to see one example to show how the sum of the three interior angles of a triangle is determined.
- Find a printed copy of a scalene triangle, or draw one on a sheet of paper. Label each angle as 1, 2, and 3.
- Cut the triangle out, and tear or cut each of the three corners (see figure below).
- Draw a horizontal line, and arrange the triangle corners so that they sit on this line as shown below.
What is the angle measure of a line which is also called a straight angle?
- If all three angles from the triangle form a line, then what is the sum of the angles in a triangle?