已知x2-xy=60,xy-y2=40,求代数式x2-y2和x2-2xy+y2的值.

问题描述:

已知x2-xy=60,xy-y2=40,求代数式x2-y2和x2-2xy+y2的值.

∵x2-xy=60,xy-y2=40,
∴x2-y2=(x2-xy)+(xy-y2)=100.
x2-2xy+y2=(x2-xy)-(xy-y2)=20.