6
1)x-(x²+y²)/(x+y)=(x²+xy-x²-y²)/(x+y)=y(x-y)/(x+y)
2)1/y+2/(x-y)=(x-y+2y)/(x-y)=(x+y)/y(x-y)
3)y(x-y)/(x+y)*(x+y)/y(x-y)=1
7
1)(a²-b²)/(a-b)-(a²+b²)/(a+b)=(a³+a²b-ab²-b³-a³-ab²+a²b+b³)/(a-b)(a+b)=
=(2a²b-2ab²0/(a-b)(a+b)=2ab/(a+b)
2)2ab/(a+b)*2/ab=4/(a+b)
14
1)3+a-18/(3-a)=(9-a²-18)/(3-a)=-(a²+9)/(3-a)=(a²+9)/(a-3)
2)(a²+9)/(a-3)² *(a-3)/(a²+9) * (a-3)=1