1)x²/y-y²/x=(x³-y³)/xy
2)1/(x+y)*(x³-y³)/xy=(x³-y³)/[xy(x+y)]
3)(x-y)(x+y)/xy-(x-y)(x²+xy+y²)/[xy(x=y)]=(x-y)*[(x+y)²-(x²+xy+y²)]/[xy(x=y)]=
=(x-y)(x²+2xy+y²-x²-xy-y²)/[xy(x-y)]=(x-y)*xy/[xy(x+y)]=(x-y)/(x+y)
4)(x-y)/(x+y):(x-y)/x=(x-y)/(x+y)*x/9x-y)=x/(x+y)