1)5xy(2x-y)/5y=x(2x-y)=8(2*8-15)=8
2)(x(y-1)-(y-1))/(x-1)=(x-1)(y-1)/(x-1)=y-1
3)(x+5)^2/x(x+5):(x-5)(x+5)/x^3=(x+5)/x*x^3/(x-5)(x+5)=x^2/(x-5)
(x/(x-1)-1) * xy-y/x = (x/(x-1) - (x-1)/(x-1) * xy - y/x = (x - x + 1)/(x-1) * xy - y/x = 1/(x-1) * xy - y/x = xy/(x-1) - y(x) = xy*x/(x-1) - y*(x-1)/x = (x^2y - xy + y) / (x-1)
8+y<4y+3; y-4y<-8+3: -3y< -5; y> -1,66
2y-7>=y+2; 2y-y>=7+2; y>= 5; y.= 5
Надеюсь, что правильно