Double Angle Formulae for Sine and Cosine

This is part of the QCE Specialist Maths course. In this post, we learn to prove and solve double angle formulae for sine and cosine.

Here are the formulae:

sin(2x) = 2 sin(x) cos(x)

cos(2x) = cos^2(x) -sin^2(x)

cos(2x) = 1 -2sin^2(x)

cos(2x) = 2cos^2(x) -1

tan(2x) = \frac{2tan(x)}{1-tan^2(x)}

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