You can find complementary angles all around you! Two angles are complementary when they add up to 90 degrees (a right angle.) Remember, a right angle looks like the angle on the right.

The angles in the flap of an envelope from the corner (each side measured from each corner) are complementary angles (A° and B°.) These angles add up to 90°, thus forming complementary angles.

In the second figure of the arrow, the angles made at the pointer head (C° and D°) are complementary as well!

The two angles don't have to be adjacent (next to one another) so long as the total of the angles is 90 degrees.

Take a look at the two angles below. They both add up to 90° (40° + 50° = 90°, however, the angle on the left is an adjacent angle (two angles that have a common vertex and a common side.) The angles on the right are not adjacent (they do not share a common vertex or a common side), but the two angles still add up to 90°!

Here are two angles that are complementary. They aren't together, but they are still complementary because they both add up to 90 degrees.

These two are complementary because 27° + 63° = 90°.

It's easy to find the missing angle in a set of complementary angles. If one of the angles is known, its complementary angle can be found by subtracting the measure of its angle from 90°.

For example, find the complementary

angle below (angle x).

Let's try another one where the two angles aren't adjacent (next to each other). Look at the angles to the right. You know that angle JKL is 34°, so all you need to do to find the angle for GHI is to subtract as follows:

90° – 34° = 56°

Therefore, angle GHI is 56°!

Click here to watch a video on how to find complementary angles.

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