<img src="https://d5nxst8fruw4z.cloudfront.net/atrk.gif?account=iA1Pi1a8Dy00ym" style="display:none" height="1" width="1" alt="" />
Dismiss
Skip Navigation
You are viewing an older version of this Concept. Go to the latest version.

Supplementary Angles

Two angles that add to 180 degrees.

Atoms Practice
Estimated4 minsto complete
%
Progress
Practice Supplementary Angles
Practice
Progress
Estimated4 minsto complete
%
Practice Now
Supplementary Angles

What if you were given two supplementary angles? How would you determine their angle measures? After completing this Concept, you'll be able to use the definition of supplementary angles to solve problems like this one.

Watch This

CK-12 Foundation: Chapter1SupplementaryAnglesA

James Sousa: Supplementary Angles

Guidance

Two angles are supplementary when they add up to \begin{align*}180^\circ\end{align*}180. Supplementary angles do not have to be congruent or touching.

Example A

The two angles below are supplementary. If \begin{align*}m \angle MNO = 78^\circ\end{align*}mMNO=78 what is \begin{align*}m \angle PQR\end{align*}?

Set up an equation.

\begin{align*}78^\circ + m \angle PQR = 180^\circ\\ m \angle PQR = 102^\circ\end{align*}

Example B

What are the measures of two congruent, supplementary angles?

Supplementary angles add up to \begin{align*}180^\circ\end{align*}. Congruent angles have the same measure. Divide \begin{align*}180^\circ\end{align*} by 2, to find the measure of each angle.

\begin{align*}180^\circ \div 2 = 90^\circ\end{align*}

So, two congruent, supplementary angles are right angles, or \begin{align*}90^\circ\end{align*}.

Example C

Name one pair of supplementary angles in the diagram below.

One example is \begin{align*} \angle INM\end{align*} and \begin{align*} \angle MNL\end{align*}.

Watch this video for help with the Examples above.

CK-12 Foundation: Chapter1SupplementaryAnglesB

Vocabulary

Two angles are supplementary when they add up to \begin{align*}180^\circ\end{align*}.

Guided Practice

Find the measure of an angle that is supplementary to \begin{align*}\angle ABC\end{align*} if \begin{align*}m \angle ABC\end{align*} is

1. \begin{align*}45^\circ\end{align*}

2. \begin{align*}118^\circ\end{align*}

3. \begin{align*}32^\circ\end{align*}

4. \begin{align*}x^\circ\end{align*}

Answers:

1. \begin{align*}135^\circ\end{align*}

2. \begin{align*}62^\circ\end{align*}

3. \begin{align*}148^\circ\end{align*}

4. \begin{align*}180-x^\circ\end{align*}

Interactive Practice

Practice

Find the measure of an angle that is supplementary to \begin{align*}\angle ABC\end{align*} if \begin{align*}m\angle ABC\end{align*} is:

  1. \begin{align*}112^\circ\end{align*}
  2. \begin{align*}15^\circ\end{align*}
  3. \begin{align*}97^\circ\end{align*}
  4. \begin{align*}81^\circ\end{align*}
  5. \begin{align*}57^\circ\end{align*}
  6. \begin{align*}(x-y)^\circ\end{align*}
  7. \begin{align*}(x+y)^\circ\end{align*}

Use the diagram below for exercises 8-9. Note that \begin{align*}\overline{NK} \perp \overleftrightarrow{IL}\end{align*}.

  1. Name another pair of supplementary angles.
  1. If \begin{align*}m\angle INJ = 63^\circ\end{align*}, find \begin{align*}m\angle JNL\end{align*}.

For exercises 10-13, determine if the statement is true or false.

  1. Supplementary angles add up to \begin{align*}180^\circ\end{align*}.
  2. Two angles on a straight line are supplementary angles.
  3. To be supplementary, two angles must be touching.
  4. It's possible for two angles in a triangle to be supplementary.

For 14-15, find the value of \begin{align*}x\end{align*}.

Vocabulary

Supplementary angles

Supplementary angles

Supplementary angles are two angles whose sum is 180 degrees.

Image Attributions

Explore More

Sign in to explore more, including practice questions and solutions for Supplementary Angles.
Please wait...
Please wait...

Original text