Menu

English

Is There Enough?

Part of the Angles section of Coddy's Geometry journey. Lesson 39 of 63.

Before chasing, ask whether the figure fixes the angle at all. A value is fixed only if a chain of rules runs from the known angles to it. If the chain breaks somewhere, the angle could be many sizes and no amount of work finds it.

$Two lines that look parallel but carry no chevrons, cut by a transversal: 70 degrees and an unknown$

Here the lines look parallel, but carry no chevrons and no ∥ statement. Without them none of the parallel rules apply, so nothing links the top crossing to the bottom one: the ? could be any size. The answer is No, and a Yes would be a guess dressed as a fact.

The same check works for anything you meet. Ask which rule would carry the known value to the next angle, and whether that rule's conditions are marked in the figure.

Challenge

AB ∥ CD, cut by two transversals: GH through E and F, and NQ through K and M. Can the angle marked ? be found from what the figure states? Answer, then press Check.

Try it yourself

$Is there enough information?$

Is there enough information?

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 Degrees and the Full Turn Acute, Right, Obtuse Adding Adjacent Angles Recap: Adjacent Angles

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

2Angles on a Straight Line

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

8Angle Chases

Verticals Meet ParallelsIs 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