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Which Rule Is It

Part of the Angles section of Coddy's Geometry journey. Lesson 35 of 62.

Identify the angle pair before writing an equation. For parallel lines, corresponding angles (the F shape) and alternate angles (the Z shape) are equal. Co-interior angles (the C shape) add to 180°.

$Co-interior angles: y plus 30 degrees and 80 degrees$

The marked angles lie between parallel lines on the same side of the transversal. They are co-interior angles, so their measures add to 180°: (y + 30) + 80 = 180.

Challenge

Medium

The marked angles sit between the parallels on opposite sides of the transversal: (x + 35)° and 110°.

$Alternate angles between two parallel lines: x plus 35 degrees and 110 degrees$

Write the equation the figure states. Do not solve it.

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

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 Angles Adding Adjacent Angles Degrees 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 AnglesWhich Rule Is ItRecap: 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