Write the Equation

Part of the Angles section of Coddy's Geometry journey. Lesson 6 of 59.

Angles on a straight line add up to 180°. This is still true when a label has a letter in it. Then you can write an equation.

$A ray on a straight line making angles of x plus 30 degrees and 70 degrees$

$\left(x+30\right)+70 = 180$

Add the numbers: $30+70 = 100$ . So $x+100 = 180$ , and $x = 80$ . The angle is $80+30 = 110$ degrees.

Challenge

A ray stands on a straight line. It makes angles of (x + 25)° and 67°. 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 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 AnglesWrite the EquationRecap: 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