Properties of Triangles
A. Find the sum of the angles in these triangles.
In all three triangles, the sum of the measures of the angles is 180°. This is a property of all triangles.
The sum of the measures of the three angles of a triangles is always 180°.
You can check this out for yourself.
- Draw and cut out a triangle.
- Colour the three angles of the triangle.
- Tear off the three corners of the triangle.
- Place them together like this.
All three pieces fit together to from a straight angle.
∠1 + ∠2 + ∠3 = 180°
Look at triangles ABC. The measures of ∠A and ∠B are given. What is the measure of ∠C ?
In ΔABC, ∠A + ∠B = 60° + 80° = 140°
The sum of three angles of a triangle is 180°
So, ∠C = 180° – 140° = 40°
Answer: ∠C = 40°