Supplementary angles are two angles 
and 
whose measures satisfy 
, the measure of a straight
angle. Equivalently, their measures sum to 
radians.
When measured in degrees, the supplement of an angle 
with 
is 
. When measured in radians,
it is 
.
The only angle supplementary to itself is the right
angle 
radians.
Supplementary angles need not be adjacent. If the two angles are adjacent, they form a linear pair. Each pair of opposite angles of a cyclic quadrilateral is also supplementary.
The illustration gives an adjacent realization. It shows the adjacent angles 
and 
,
which together form the straight angle 
.
