## Quick Reference

(in trigonometry)

A formula in trigonometry that expresses a function of a double angle in terms of the single angle. This can be obtained from the corresponding compound angle formulae by substituting *A*=*B*=*x*:

sin (2*x*) = 2 sin *x* cos *x*,

cos (2*x*) = cos^{2}*x* − sin^{2}*x*

*Subjects:*
Mathematics.

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