5y/4 - x/4 (2x-y) , если x-y = 6
[m]\frac{5y}{4}-\frac{x}{4}-(2x-y)=\frac{5y}{4}-\frac{x}{4}-2x+y=(\frac{5y}{4}+y)-(2x-\frac{x}{4})=\frac{9y}{4}-\frac{9x}{4}=\frac{9}{4}(y-x)=\frac{9}{4}\cdot (-6)=-13\frac{1}{2}[/m] x-y=6 тогда -(x-y)=-6 y-x=-6