Supplementary Angles
Two Angles are Supplementary if they add up to 180 degrees.
These two angles (140° and 40°) are Supplementary Angles, because they add up to 180°. Notice that together they make a straight angle. 



But the angles don't have to be together.
These two are supplementary because 60° + 120° = 180° 



If the two angles add to 180°, we say they "Supplement" each other.
Supplement comes from Latin supplere, to complete or "supply" what is needed. 





Spelling: be careful, it is not "Supplimentary Angle" (with an "i") 
Complementary vs Supplementary
A related idea is Complementary Angles, they add up to 90°
How can you remember which is which? Easy! Think:
 "C" of Complementary stands for "Corner" (a Right Angle), and
 "S" of Supplementary stands for "Straight" (180 degrees is a straight line)
