Three Angles on a Line
Part of the Angles section of Coddy's Geometry journey. Lesson 9 of 62.
Two rays divide the straight angle into three adjacent parts. Their measures add to 180°. The same rule applies to any number of adjacent angles that together form a straight angle.
In the figure, x + (50 + 70) = 180: the canvas brackets the known parts together because they are the first thing to deal with. Gather them, 50 + 70 is 120, so x + 120 = 180 and x = 60. With three or more parts, the winning first move is always the same: gather every number before touching the x.
Challenge
EasyTwo rays split the straight line in the figure into three angles: 40°, x° and 75°.
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 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