First, let’s review what a triangle is. A triangle is a closed shape that has three sides and three angles. The three angles of a triangle always add up to 180 degrees. This means that if we know the measure of two angles in a triangle, we can figure out the measure of the third angle by subtracting the sum of the two known angles from 180 degrees.

Now, let’s look at some examples of triangle worksheets. On these worksheets, you’ll see different triangles with some angles already labeled with their measures. Your job is to find the size of the unknown angles in each figure.

To do this, you’ll need to use what we just learned about the sum of the angles in a triangle. You can start by adding together the measures of the angles that are already labeled. Then, subtract that sum from 180 degrees to find the measure of the unknown angle.

For example, let’s say we have a triangle with two angles labeled: one is 40 degrees and the other is 80 degrees. To find the measure of the third angle, we add 40 degrees and 80 degrees together: 40 + 80 = 120. Then, we subtract that sum from 180 degrees: 180 – 120 = 60. So the unknown angle in this triangle is 60 degrees.

You’ll repeat this process for each triangle on the worksheet. Remember, the sum of the angles in a triangle always adds up to 180 degrees. So, if you know the measures of two angles in a triangle, you can find the measure of the third angle by subtracting the sum of the two known angles from 180 degrees.

A triangle is a three-sided polygon. The sum of the lengths of the sides of a triangle is always greater than the length of the third side. The angles of a triangle always add up to 180 degrees.

Get an angle on triangles with this practice worksheet! Use this worksheet to practice the theorem sum of the interior angles of a triangle is 180 degrees.

**Answer Key**