# Proof of the Difference Formula for Sine and of the Addition Formula for Cosine

Requires a Wolfram Notebook System

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

This Demonstration shows a proof of the difference formula for sine, and a proof of the addition formula for cosine, using the formula .

Contributed by: Izidor Hafner (March 2011)

Open content licensed under CC BY-NC-SA