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.

Pegs and Holes – 4castle

algorithm - Line-Circle Interception (point,angle) - Stack Overflow

Full Angle -- from Wolfram MathWorld

Complementary Angles -- from Wolfram MathWorld

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

How to Calculate Angle Size

Right Triangle -- from Wolfram MathWorld

Steinmetz Solid - From Wolfram MathWorld, PDF

ArcTanDegree Wolfram Function Repository