x²+y²
=[(x²+2xy+y²)+(x²-2xy+y²)]÷2
=(1+49)÷2
=50÷2
=25
xy
=[(x²+2xy+y²)-(x²-2xy+y²)]÷4
=(1-49)÷4
=-48÷4
=-12可以告诉我 为什么要除以2么？你好：请看x²+2xy+y²+x²-2xy+y²=2x²+2y²=2(x²+y²)所以要除以2谢谢我懂了你好：后面的是x²+2xy+y²-(x²-2xy+y²)=x²+2xy+y²-x²+2xy-y²=4xy所以要除以4希望能对你有帮助！