УПРОСТИТЕ :y(2 степень)+x(2 степень)-2xy________________________xz-yz+ty-xt 

\frac{y^2+x^2-2xy}{xz-yz+ty-xt}=\frac{(x-y)^2}{(xz-yz)+(ty-xt)}=\frac{(x-y)^2}{z(x-y)+t(y-x)}=\frac{(x-y)^2}{(z+t)(x-y)}=\frac{(x-y)}{(z+t)}[latex]\frac{y^2+x^2-2xy}{xz-yz+ty-xt}=\frac{(x-y)^2}{(xz-yz)+(ty-xt)}=\frac{(x-y)^2}{z(x-y)+t(y-x)}=\frac{(x-y)^2}{(z+t)(x-y)}=\frac{(x-y)}{(z+t)}[/latex]     (x-y)^2=(y-x)^2