# Cosine and Sine of the Sum of Two Angles

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The formulas for and are derived using purely geometric reasoning, avoiding the usual cumbersome algebraic manipulations. Proceed through steps 1–5 to follow the derivation.

Contributed by: Tomas Garza (July 2011)

Open content licensed under CC BY-NC-SA

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"Cosine and Sine of the Sum of Two Angles"

http://demonstrations.wolfram.com/CosineAndSineOfTheSumOfTwoAngles/

Wolfram Demonstrations Project

Published: July 1 2011