We prove the formula for sin(A-B) using right-angled triangles then we show how the corresponding formulae for cos(A-B) and sin and cos of A+B can be deduced as a result.

A Geometric proof of the sum and difference formulae for sin and cos (MathsCasts)

These MathsCasts were produced by the mathematics support centres at Swinburne University, the University of Limerick and Loughborough University. They were part of a collaborative research project to develop high quality resources and investigate the effectiveness of MathsCasts to support mathematics learning. The full set of resources are available at http://commons.swin.edu.au/s/mathscasts MathsCasts are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License

Share A Geometric proof of the sum and difference formulae for sin and cos (MathsCasts)

Sign up to save your podcasts

A Geometric proof of the sum and difference formulae for sin and cos (MathsCasts)

A Geometric proof of the sum and difference formulae for sin and cos (MathsCasts)