原式=(x²+y²)(x²-y²)/[x(x²+y²)+y(x²+y²)]=(x²+y²)(x+y)(x-y)/[(x+y)(x²+y²)]=x-y=1
2007/2008x1004+2007/2008x1005—2007/2008=2007/2008x(1004+1005-1)=2007/2008x2008=2007103541323663103
