Straight Angle -- from Wolfram MathWorld

A straight angle is an angle equal to 180 degrees=pi radians. Two right angles make a straight angle, and two straight angles make a full angle.

Lesson Angle in a semicircle

Trigonometry -- from Wolfram MathWorld

Conic Sections - Wakelet

Isosceles Right Triangle -- from Wolfram MathWorld

Programming with triangles! - #16 by jremington - Programming

Deceptively simple geometry problem. : r/math

ASS Theorem -- from Wolfram MathWorld

Steinmetz Solid - From Wolfram MathWorld, PDF, Mathematics

Angle Trisection: A Math Problem Claimed to Not be Solvable and

Pat'sBlog: 2013

Right Angle -- from Wolfram MathWorld

45-45-90 and 30-60-90 Triangles