Double Angle Identity

Derived from Compound Angle Identity Literally just make x = y. $sin(2x)=2sin(x)cos(x)$ $cos(2x)=co{s}^2(x)-si{n}^2(x)$ $cos(2x)=1-2si{n}^2(x)$ $cos(2x)=2co{s}^2(x)-1$ $tan(2x)=2tan(x)/(1-ta{n}^2(x))$