Trig Identities

Product-to-Sum Formulae

$$\cos (A)\cos (B)=\frac{1}{2}\cos (A-B)+\frac{1}{2}\cos (A+B)$$ $$\sin (A)\cos (B)=\frac{1}{2}\sin (A-B)+\frac{1}{2}\sin (A+B)$$ $$\sin (A)\sin (B)=\frac{1}{2}\cos (A-B)-\frac{1}{2}\cos (A+B)$$