36-у^2/у-8 * (у/у-6 - 2 у/у^2-12 у+36) + 12 у/у-6

(6-y) (6+y) / (y-8) (y / (y-6) - 2y / (y-6) ^2) + 12y / (y-6) =

= (6-y) (6+y) / (y+8) * (y^2-8y) / (y-6) ^2 + (12-y) / (y-6) =

=-y (6+y) / (y-6) + 12y / (y-6) = (-6y-y^2+12y) / (y-6) = (6y-y^2) / (y-6) = y (6-y) / (y-6) = - y