(1-2cos(x/2)+cosx)/(1+2cos(x/2)+cosx) = ?

[latex] \frac{1-2cos \frac{x}{2}+cosx }{1+2cos \frac{x}{2}+cosx } = \frac{1+cosx-2cos \frac{x}{2} }{1+cosx+2cos \frac{x}{2} } = \frac{2cos^{2} \frac{x}{2}-2cos \frac{x}{2} }{2cos^{2} \frac{x}{2}+2cos \frac{x}{2} } = \\ \frac{2cos \frac{x}{2}(cos \frac{x}{2} -1) }{2cos \frac{x}{2}(cos \frac{x}{2}+1) }= \\ \frac{-2sin^{2} \frac{x}{4} }{2cos^{2} \frac{x}{4} } =-tg^{2} \frac{x}{4} [/latex]