# Supplementary Angles

Two Angles are Supplementary when 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°

## Play With It ...

(Drag the points)

images/geom-comp-supp.js?mode=supp

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

*Spelling:* be careful, it is **not***"Suppl imentary Angle"*

## Complementary vs Supplementary

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

How to remember which is which? Well, **alphabetically** they are:

- Complementary add to 90°
- Supplementary add to 180°

You can also think:

- "
**C**" of**C**omplementary is for "**C**orner" (a Right Angle), and - "
**S**" of**S**upplementary is for "**S**traight" (180° is a straight line)

Or you can think:

- when you are
**right**you get a**compliment**(sounds like compl**e**ment) - "supplement" (like a vitamin supplement) is something extra, so is bigger

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