To simplify cos(x+2pi)/sinxcos(x+2π)sinx, first one may note that adding 2pi2π or its multiple, to a trigonometric ratio, does not change its value
i.e. sin(x+2npi)=sinxsin(x+2nπ)=sinx (for all nn, where nn is an integer), cos(x+2npi)=cosxcos(x+2nπ)=cosx, tan(x+2npi)=tanxtan(x+2nπ)=tanx, cot(x+2npi)=cotxcot(x+2nπ)=cotx, sec(x+2npi)=secxsec(x+2nπ)=secx and csc(x+2npi)=cscxcsc(x+2nπ)=cscx.
Hence, cos(x+2pi)/sinxcos(x+2π)sinx = cosx/sinxcosxsinx or cotxcotx.