Finding the Apex
Part of the Angles section of Coddy's Geometry journey. Lesson 48 of 62.
Turn it around: the ticks reveal that the two base angles match, so seeing one base angle means knowing both. The apex then takes whatever the budget has left.
In the figure one base angle reads 70°, and the ticks copy it across: y + (70 + 70) = 180. Gather 140, and y = 40. The ticks did half the work before the algebra began.
Challenge
EasyThe ticked sides make the triangle isosceles; each base angle measures 55°, and the apex measures x°.
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 Pairs10Isosceles Triangles
Base Angles Are EqualFinding the ApexWhich Angles MatchEquilateral AnglesIsosceles at WorkRecap: Twin Corners2Straight 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