# Proof without Words: $\sin(x+y) = \sin x \cos y + \cos x \sin y$ for $x+y < \pi$

by Sidney H. Kung (Jacksonville University)

Mathematics Magazine
April, 1991

Subject classification(s): Geometry and Topology | Geometric Proof | Trigonometry | Trigonometric Identities
Applicable Course(s): 2.2 Trigonometry | 2.3 College Algebra & Trigonometry combined | 4.1 Introduction to Proofs

The author presents a geometric proof of the trigonometric identity for the sine of the sum of angles.

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