Angle Trisection -- from Wolfram MathWorld

Angle trisection is the division of an arbitrary angle into three equal angles. It was one of the three geometric problems of antiquity for which solutions using only compass and straightedge were sought. The problem was algebraically proved impossible by Wantzel (1836). Although trisection is not possible for a general angle using a Greek construction, there are some specific angles, such as pi/2 and pi radians (90 degrees and 180 degrees, respectively), which can be trisected. Furthermore

Equal Parallelians Point -- from Wolfram MathWorld

Angle Trisection: A Math Problem Claimed to Not be Solvable and Has Not Been Solved for Over 2200 Years is Solved by Mahesh Bubna in 2022

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Angle -- from Wolfram MathWorld

Angle Trisection -- from Wolfram MathWorld

Angle Trisection -- from Wolfram MathWorld

Bisection - Wikiwand

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Angle Trisection: A Math Problem Claimed to Not be Solvable and Has Not Been Solved for

Remembering Martin Gardner—Wolfram