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.

Pentaflake, in Google SketchUp - 3DVinci

Orthocenter -- from Wolfram MathWorld

Concurrent lines - Wikipedia

Parallelogram - Wikipedia

Sine Encyclopedia MDPI

Schoute Center -- from Wolfram MathWorld

Isosceles Right Triangle -- from Wolfram MathWorld

Angle Standard Position -- from Wolfram MathWorld

All I have is 3 points in a coordinate system. How can I calculate