# Interior Angles Of A Triangle

In these lesson, we will learn

• about interior angles of triangles
• the properties of the interior angles of a triangle
• how the properties can be used to find the missing angles inside a triangle
• how the sum of interior angles of a triangle can be used to set up equations.

The following diagram shows that the sum of angles in a triangle is 180°. Scroll down the page for more examples and solutions on how to find missing angles in a triangle. ### Interior Angles

The interior angles of a triangle are the angles inside the triangle.

### Properties of Interior Angles

• The sum of the three interior angles in a triangle is always 180°.
• Since the interior angles add up to 180°, every angle must be less than 180°. ### Find missing angles inside a triangle

Example:
Find the value of x in the following triangle. Solution:
x + 24° + 32° = 180° (sum of angles is 180°)
x + 56° = 180°
x = 180° – 56° = 124°

How to find the missing angle inside a triangle.

Example:
Find the missing angle in a triangle.
A = 15°, B = ?, C = 92°

### Using Interior Angles Of Triangle To Set Up Equations

How to use the sum of the interior angles of a triangle to solve problems?

Example:

1. Write an equation and solve for the unknown.
2. Substitute your answer into each expression to determine the measure of the angles.

Using the sum of the interior angles of a triangle, write an equation and solve for the unknown.

Try the free Mathway calculator and problem solver below to practice various math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations. 