# Complementary Angles

**Definition:** Any two angles are called Complementary angles when they add up to 90°. When two angles add to 90°, we say that the angles are “Complement” to each other. In the pair of Complementary angles if one angle is x°, then its Complement is an angle of (90 - x)° .

From the above figures, we have $\angle$ABD and $\angle$DBC are complementary because 30° + 60° = 90°. $\angle$FGH and $\angle$IJK are complementary because 40.2° + 49.8° = 90°. Also, $\angle$ABD and $\angle$DBC together form right angle $\angle$ABC. Thus, if two angles are together and are complement to each other then they have a common vertex and share one side and are called Adjacent complementary angles. The other two non-shared sides of the angles form right angle. The angles need not be together, but together they add up to 90°. This can be seen from $\angle$FGH and $\angle$IJK. They are called non-adjacent complementary angles.

Two angles are complementary, only when both are acute angles.