已知x方-xy=60,xy-y方=40,求代数式x方-y方和2x方-5xy+3y方的值.ps：

题目

已知x方-xy=60,xy-y方=40,求代数式x方-y方和2x方-5xy+3y方的值.ps：

答案

x方-y方
=x²-xy+xy-y²
=(x²-xy)+(xy-y²)
=60+40
=100
2x方-5xy+3y方
=2x²-2xy-3xy+3y²
=2(x²-xy)-3(xy-y²)
=120-120
=0