Alternate Angles
Part of the Angles section of Coddy's Geometry journey. Lesson 33 of 62.
Now look between the parallels, on opposite sides of the transversal: the Z shape. These are alternate angles, and with parallel lines they too are equal. Why: the alternate angle is the corresponding angle’s vertical twin, and both of those moves preserve the measure.
In the figure the 55° and z° tuck into the Z’s two corners, so z = 55. Spot the Z (sometimes mirrored into an S) and the two angles in its bends match.
Challenge
EasyThe marked angles are alternate: (3x - 15)° and 60°.
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 Crossing7Crossing Parallel Lines
Parallel LinesCorresponding AnglesAlternate AnglesCo-interior AnglesWhich Rule Is ItRecap: The Three Pairs2Straight 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 Turn3Right 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