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Across the Crossing

Part of the Angles section of Coddy's Geometry journey. Lesson 4 of 59.

$Two lines crossing at B. One angle is 70 degrees, and the angle facing it across B is unknown$

Two straight lines cross at B. They make four angles. Look at the 70° angle. It has two neighbours. A neighbour is the angle right next to it. They share one side, called an arm. The 70° angle and each neighbour lie on one straight line.

The angle across from it, tip to tip, shares no arm with it. You will learn about that angle soon.

Challenge

Lines AC and DE cross at B. ∠CBD is 128°. Its neighbour ∠EBC is x°. Find x. Tap the two angles and pick the reason. Then solve for x and press Check.

Try it yourself

$Use the figure to find x$

Use the figure to find x

All lessons in Angles

1Meet the Angle

Your First Angle Angles on a Line Degrees and the Full TurnAcross 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