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Equilateral Angles

Part of the Angles section of Coddy's Geometry journey. Lesson 47 of 59.

A triangle with all three sides equal is equilateral. It is isosceles three ways over: every pair of sides is equal, so every pair of angles is equal, and all three angles match. Three equal angles share 180°, so each is 60°.

$An equilateral triangle KLM, every side ticked and every angle 60 degrees$

That makes 60° a fact you can read straight off the ticks, like 90° off a square. On the board the rule is Equilateral triangle. Once you have a 60° angle, the other rules carry it on, exactly as they would a labelled one.

Challenge

Triangle ABC has all three sides ticked, and the side AB is extended past B to D. Find the angle marked ?, giving every step its rule, then press Check.

Try it yourself

$Find the marked part of the figure$

Find the marked part of the figure

All lessons in Angles

1Meet the Angle

Your First Angle Angles on a Line Degrees 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 MatchEquilateral AnglesIsosceles 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