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Adding Adjacent Angles

Part of the Angles section of Coddy's Geometry journey. Lesson 3 of 62.

Adjacent angles sit side by side: they share a vertex and one arm, without overlapping. Their measures simply add: part plus part makes the whole. That sounds obvious, and it is exactly why it is powerful: know the whole and one part, and the other part is forced.

$An angle of 65 degrees split into 25 degrees and x degrees$

In the figure the whole ∠AVB is 65° and the part ∠AVM is 25°, so the other part obeys x + 25 = 65. An equation is a balance: do the same thing to both sides and it stays true. Take 25 from both sides and x stands alone: x = 40. On the canvas that is one move, and it is the move this whole journey runs on.

Challenge

Easy

In the figure, ∠AVM measures 30° and the whole angle ∠AVB measures 80°.

$An 80 degree angle split into 30 degrees and x degrees$

Find x, the measure of ∠MVB.

Try it yourself

x + 30 = 80

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

1Meet the Angle

Your First Angle Naming AnglesAdding Adjacent AnglesDegrees and the Full Turn Acute, Right, Obtuse Recap: Adjacent Angles

4Vertical Angles

Linear Pairs Vertical Angles Are Equal Solving with Verticals All Four Angles Recap: At the Crossing

7Crossing Parallel Lines

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

10Isosceles Triangles

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

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 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