Purple Math
Purplemath: Conventions
A "convention" is "just the way a thing is done!". This reference material lists some common conventions (notational assumptions) for geometry and trigonometry.
Purple Math
Purplemath: The Pythagorean Theorem
Defines the Pythagorean Theorem, and demonstrates how to use this Theorem in connection with right-angled triangles.
Purple Math
Purplemath: Sectors, Areas, and Arcs
Explains formulas for areas of sectors of circles and lengths of arcs. Demonstrates how to use the formulas in each of degrees and radians.