Math is Fun

Math is Fun Home PageHOME

A-Z Listing



Top-rated teacher Web sites rated by teacher usage
Edunet site of the week January 2001
Maths Is Fun is ICRA Registered
Copyright © 2006
MathsIsFun.com

Supplementary Angles

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


These two angles (140° and 40°) are Supplementary Angles, beacuse 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")

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

(How can you remember that Complementary is 90° and Supplementary is 180°? Luckily "C" comes before "S" in the alphabet and 90 comes before 180. That's what I do.)