Two angles 
and 
for which 
are said to be supplementary. In other words,
and 
are supplementary angles if they produce a straight
angle when combined.
Supplementary Angles
See also
Angle, Complementary Angles, Digon, Straight Angle Explore this topic in the MathWorld classroomExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Supplementary Angles." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/SupplementaryAngles.html