UHG39: Rational trigonometry: an overview:
(Rational number only)
This is a revolutionary approach (2005) to teach Secondary / High school Trigonometry by using purely algebra, no geometry and no picture, no sine, cosine, tangent, etc.
New concepts:
Vector as an order pair (x, y)
Quadrance = magnitude of vector
Perpendicular of 2 vectors
Parallel
Spread (angle between 2 vectors)
Amazon Book by the Dr. NJ Wildburger:
Mathtuition88 
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