A Visual Proof of the Double-Angle Formula for Sine

Initializing live version
Download to Desktop

Requires a Wolfram Notebook System

Interact on desktop, mobile and cloud with the free Wolfram Player or other Wolfram Language products.

The double-angle formula for sine states that . Computing the area of a triangle using the formula (area equals one-half base times height) gives for the top triangle and for the bottom triangle.

Contributed by: Chris Boucher (March 2011)
Open content licensed under CC BY-NC-SA



This image is from J. D. Currie, "Proof without Words: Double Angle Formula via Area," Mathematics Magazine, 81(1), 2008 p. 62.

Feedback (field required)
Email (field required) Name
Occupation Organization
Note: Your message & contact information may be shared with the author of any specific Demonstration for which you give feedback.