Alternate with Algebra
Part of the Angles section of Coddy's Geometry journey. Lesson 40 of 62.
An equal-type pair with expressions on both sides lands you in familiar algebra: unknowns on both sides of the equals sign. Collect the x terms on one side, the numbers on the other, exactly as with vertical angles in chapter 4.
The figure’s Z pair gives 3y + 10 = y + 70. Take y from both sides: 2y + 10 = 70. Take 10, divide by 2: y = 30. Both labels then read 100°, one number from two disguises.
Challenge
MediumTwo parallel lines are cut by a transversal. The marked angles measure (4x - 30)° and (2x + 40)°.
Find x.
Try it yourself
Solve for x
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Angles
1Meet the Angle
Your First AngleNaming AnglesAdding Adjacent AnglesDegrees and the Full TurnAcute, Right, ObtuseRecap: Adjacent Angles4Vertical Angles
Linear PairsVertical Angles Are EqualSolving with VerticalsAll Four AnglesRecap: At the Crossing2Straight Lines and Supplements
Angles on a LineSupplementary AnglesThree Angles on a LineWrite the EquationRecap: Along the Line5Around a Point
Angles Around a PointThe Missing AngleEqual SlicesFour Angles, One PointRecap: The Full Turn8Transversal Problems
Both Angles LabeledVerticals Meet ParallelsFrom Figure to EquationAlternate with AlgebraRecap: Through the Strip3Right Angles and Complements
Complementary AnglesFinding the ComplementPerpendicular LinesEqual Parts of a CornerRecap: The Right Corner6The Angle Bisector
The Angle BisectorBisected ExpressionsBisecting a Straight AngleRecap: Split in Half