Definition: Complementary angles are two angles whose measures add up to 90 degrees, and together they form a right angle when placed side by side.
What are complementary angles?
Two angles are complementary when their measures sum to 90 degrees. They can be adjacent, forming a corner, or separate.
How do you find a missing one?
Subtract from 90. If one angle is 38 degrees, its complement is 52 degrees. Both are acute, because each must be less than 90.
How do you solve with algebra?
Suppose two complementary angles measure (4x + 5) degrees and (6x – 15) degrees. Their sum is 10x – 10 = 90, so 10x = 100 and x = 10. The angles are 45 and 45 degrees.
Where do you see them?
In the corner of a picture frame or where a ladder leans against a wall. If Mathbot leans a ladder so the angle with the ground is 70 degrees, the angle between the ladder and the wall is 20 degrees.
How do you remember it?
Complementary comes with c, like corner, a 90 degree corner. Supplementary comes with s, like straight line.
What is a common mistake?
Using 180 instead of 90. Check that both answers are acute.