ДОКАЖИТЕ ТОЖДЕСТВО Х-1/Х+6:(3/х+6 + 5х+2/х^2+5х-6 - х/х-1)=-1

Решите задачу:

$\frac{x-1}{x+6} :\bigg( \frac{3}{x+6}+ \frac{5x+2}{x^2+5x-6}- \frac{x}{x-1} \bigg)= \frac{x-1}{x+6} :\bigg( \frac{3}{x+6}+ \frac{5x+2}{(x+6)(x-1)}-\frac{x}{x-1} \bigg)=\\\\\\=\frac{x-1}{x+6} :\bigg( \frac{3(x-1)+5x+2-x(x+6)}{(x+6)(x-1)} \bigg)=\frac{x-1}{x+6} : \frac{-x^2+2x-1}{(x+6)(x-1)} = \frac{x-1}{x+6} : \frac{-(x-1)^2}{(x+6)(x-1)} =\\\\\\=\frac{x-1}{x+6} : \frac{-(x-1)}{(x+6)} = -\frac{(x-1)(x+6)}{(x+6)(x-1)} =-1$