1)=(x-y)(x-y) - y(x+y)  /(x+y)(x-y) =x²-2xy+y²-xy-y² /x²-y²=x²-3xy /x²-y²
2)=3a²+6a/(a-3)(a+3) -2a/a-3=3a²+6a-2a(a+3) /(a-3)(a+3)=3a²+6a-2a²-6a/a²-9=
=a²/a²-9
3)=4a(a+3)-4a²+36 /a+3=4a²+12a-4a²+36/a+3=12a+36/a+3=12(a+3)/a+3=12