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Supplementary Angles

Part of the Angles section of Coddy's Geometry journey. Lesson 8 of 62.

Two angles whose measures add to 180° are supplementary: together they would fill a straight line. They do not need to touch. Supplementary is a fact about the two numbers, wherever the angles sit.

$Two separate supplementary angles, 110 and 70 degrees$

The pair in the figure obeys 110 + 70 = 180, so they are supplements even though they stand apart. Given one, the other is forced: the supplement of 110° is 180 - 110, which is 70°.

Challenge

Easy

The two angles in the figure are supplementary. One measures 65°.

$Two supplementary angles, 65 degrees and x degrees$

Find x.

Try it yourself

x + 65 = 180

Solve for x

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Angles

2Straight Lines and Supplements

Angles on a LineSupplementary AnglesThree Angles on a Line Write the Equation Recap: Along the Line

5Around a Point

Angles Around a Point The Missing Angle Equal Slices Four Angles, One Point Recap: The Full Turn

8Transversal Problems

Both Angles Labeled Verticals Meet Parallels From Figure to Equation Alternate with Algebra Recap: Through the Strip

11The Exterior Angle

The Exterior Angle Using the Shortcut Two Roads, One Answer Exterior in the Wild Recap: Outside View

3Right Angles and Complements

Complementary Angles Finding the Complement Perpendicular Lines Equal Parts of a Corner Recap: The Right Corner

6The Angle Bisector

The Angle Bisector Bisected Expressions Bisecting a Straight Angle Recap: Split in Half

9Triangle Angle Sum

The 180 Rule Finding the Third Angle Two Unknown Angles Right Triangles Recap: The Budget

12Final Challenges

Final: The Angle Chase Final: Triangle Meets Line Final: The Full Round Final: Isosceles Chase Final: Master of Angles