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Your First Angle

Part of the Angles section of Coddy's Geometry journey. Lesson 1 of 59.

A ray is a line that starts at a point and goes on in one direction. Here a ray stands on a straight line. It makes two angles. We measure angles in degrees, written °.

Push the ray. One angle grows and the other shrinks. One thing stays the same. Can you find it?

$A straight line AC with a ray BD standing on it, making two angles at B$

Challenge

Drag the point D until the left angle, ∠DBA, is 45°. Watch the right angle, ∠CBD, while you drag. What does it show when you stop? Then press Check.

Try it yourself

$Drag the figure and watch$

Drag the figure and watch

All lessons in Angles

1Meet the Angle

Your First AngleAngles 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 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