已知x2-xy=21,xy-y2=-12,分别求式子x2-y2与x2-2xy+y2的值.

问题描述:

已知x2-xy=21,xy-y2=-12,分别求式子x2-y2与x2-2xy+y2的值.

x2-y2=(x2-xy)+(xy-y2)=21-12=9;
x2-2xy+y2=(x2-xy)-(xy-y2)=21+12=33.