Parallel Lines
Part of the Angles section of Coddy's Geometry journey. Lesson 31 of 62.
Parallel lines run in the same direction forever and never meet. In figures, matching arrowheads drawn on the lines declare them parallel; in text the symbol is ∥, so ℓ ∥ m reads “line ℓ is parallel to line m”.
A third line that cuts across both is a transversal, and it is where the story begins: the transversal makes four angles at each crossing, eight in all, and because the parallels run in the same direction, the two crossings are copies of each other. The next lessons name the pairs that fall out.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
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