Complementary angles are two angles 
and 
whose measures satisfy 
, the measure of a right
angle. Equivalently, their measures sum to 
radians.
When measured in degrees, the complement of an angle 
with 
is 
. When measured in radians,
it is 
.
The only angle complementary to itself is 
radians. The two
acute angles of a right
triangle are complementary.
Complementary angles need not be adjacent. The illustration gives an adjacent realization. It shows the adjacent angles 
and 
, which together form the right
angle 
.
