What is a complementary angle?

What is a complementary angle?

• A. Add up to 180 degrees.
• B. Add up to 270 degrees.
• C. Add up to 90 degrees.
• D. Sum to 180 degrees.

Answer: (C)

Complementary angles are two angles whose measures add up to 90 degrees. This comes from the idea of a right angle, which measures exactly 90 degrees, so if two angles fit together inside that right angle, their measures sum to 90. For example, 30 degrees and 60 degrees are complementary, as are two angles of 45 degrees each. The other sums described—180 degrees or 270 degrees—relate to different relationships (180 degrees is a supplementary pair, not complementary). So the defining idea is that their measures add to 90 degrees.

Complementary angles are two angles whose measures add up to 90 degrees. This comes from the idea of a right angle, which measures exactly 90 degrees, so if two angles fit together inside that right angle, their measures sum to 90. For example, 30 degrees and 60 degrees are complementary, as are two angles of 45 degrees each. The other sums described—180 degrees or 270 degrees—relate to different relationships (180 degrees is a supplementary pair, not complementary). So the defining idea is that their measures add to 90 degrees.