Supplementary Angles

Two Angles are Supplementary when they add up to 180 degrees.

 

supplementary angles 40 and 140

These two angles (140° and 40°) are Supplementary Angles, because they add up to 180°:

Notice that together they make a straight angle.

 

supplementary angles 60 and 120

But the angles don't have to be together.

These two are supplementary because
60° + 120° = 180°

Play With It ...

(Drag the points)

 

speech When the two angles add to 180°, we say they "Supplement" each other.
Supplement
comes from Latin supplere, to complete or "supply" what is needed.
   
pencil and paper Spelling: be careful, it is not "Supplimentary Angle"

Complementary vs Supplementary

A related idea is Complementary Angles, they add up to 90°

How to remember which is which? Easy! Think:

You can also think "Supplement" (like a Vitamin Supplement) is something extra, so it is bigger.