The measure of an angle is 78°. What is the measure of a complementary angle?

Complementary angles add up to 90°.

It is given that one angle is 78°.

Let the other angle be x.

Therefore x+78=90

x=90-78

x=12°

First you need to know the definition of a complementary angle. That means that two angles add up to 90 degrees, or a right angle.

To find an angle complementary to a 78 degree angle, you need to subtract 78 from 90.

90 - 78 = 12