FTCE General Knowledge Math Practice Test

What are two angles called when their sum equals 90 degrees?

1. Supplementary angles

2. Adjacent angles

3. Complementary angles

4. Vertical angles

The correct answer is: Complementary angles

The correct term for two angles whose sum equals 90 degrees is complementary angles. Complementary angles can be two separate angles that add up to 90 degrees, such as a 30-degree angle and a 60-degree angle, or they can be two angles that are part of a right triangle. This relationship is significant in various geometric contexts, including trigonometry and the measurement of angles. Supplementary angles, on the other hand, refer to two angles that sum to 180 degrees. Adjacent angles are angles that share a common vertex and side but do not overlap, regardless of their measurements. Vertical angles are the angles opposite each other when two lines cross; they are always equal but do not inherently sum to a specific total. Thus, the context of measuring up to 90 degrees specifically defines them as complementary angles.