Логарифм
y=lglnctgx
Y'=[1/(lnctgx * ln10)] *[1/ctgx] *[-1/sin^2 x]=-1/(ln10*sinx*cosx*lnctgx)= =преобразуем sinx*cosx=sin2x/2= =-2/(ln10*sin2x*lnctgx)