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A Simple Geometric Proof of the Addition Formula for the Sine

by Jeffrey Li-chieh Ho (Scottsboro High School, AL)

This article originally appeared in:
College Mathematics Journal
May, 1994

Subject classification(s): Geometry and Topology | Trigonometry
Applicable Course(s): 2.2 Trigonometry

The following is a short, simple, but not well-known proof of the well-known trigonometric identify \(\sin(a+b) = \sin a \cos b + \cos a \sin b\).

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