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Angles on a Line

Part of the Angles section of Coddy's Geometry journey. Lesson 2 of 59.

When you pushed the ray, the two angles always added up to 180°. For example: 45° and 135°, or 90° and 90°. This is always true. Angles side by side on a straight line add up to 180°. This works for any number of angles on the line.

$A straight line cut by two rays into angles of 40 degrees, an unknown angle, and 55 degrees$

Here the missing angle is $180-40-55 = 85$ degrees. Two angles that add up to 180° are called supplementary. For example, 100° and 80° are supplementary.

Challenge

Two rays cut the straight line PQ into three angles: 52°, x° and 61°. Find x. Tap the three angles and pick the reason. Then solve for x and press Check.

Try it yourself

$Use the figure to find x$

Use the figure to find x

All lessons in Angles

1Meet the Angle

Your First AngleAngles on a LineDegrees and the Full Turn Across the Crossing

4Vertical Angles

Two Lines Cross Vertical Angles Are Equal Solving with Verticals All Four Angles Recap: At the Crossing

7Parallels and Transversals

Parallel Lines Corresponding Angles Alternate Angles Co-interior Angles Which Rule Is It Recap: The Three Pairs

10Isosceles and Equilateral

Base Angles Are Equal Finding the Apex Which Angles Match Equilateral Angles Isosceles at Work Recap: Twin Corners

2Naming and Equations

Adding Adjacent Angles 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

8Angle Chases

Verticals Meet Parallels Is There Enough?From Figure to Equation Both Angles Labeled 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

The Square Mark Complementary Angles Perpendicular Lines Finding the Complement 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