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Two Unknown Angles

Part of the Angles section of Coddy's Geometry journey. Lesson 44 of 62.

Two angles may be expressed using the same unknown, such as x° and 2x°. Add these expressions and the third angle, set the sum equal to 180°, and combine like terms.

$A triangle with angles 2y, y and 30 degrees$

The three angles satisfy y + 2y + 30 = 180. Combine like terms to get 3y + 30 = 180, then subtract 30 and divide by 3. This gives y = 50. The angles are 50°, 100°, and 30°, whose sum is 180°.

Challenge

Medium

The triangle’s angles are x°, 2x° and 60°.

$A triangle with angles 60, x and 2x degrees$

Find x.

Try it yourself

x + 2x + 60 = 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 Line Supplementary Angles Three 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 AngleTwo Unknown AnglesRight 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