已知x^2=21,xy-y^2=-12,分别求式子x^2-y^2与x^2-2xy+y^2的值

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已知x^2=21,xy-y^2=-12,分别求式子x^2-y^2与x^2-2xy+y^2的值已知x^2=21,xy-y^2=-12,分别求式子x^2-y^2与x^2-2xy+y^2的值已知x^2=21

已知x^2=21,xy-y^2=-12,分别求式子x^2-y^2与x^2-2xy+y^2的值
已知x^2=21,xy-y^2=-12,分别求式子x^2-y^2与x^2-2xy+y^2的值

已知x^2=21,xy-y^2=-12,分别求式子x^2-y^2与x^2-2xy+y^2的值
根据以往经验,感觉题目没抄完整,少了个-xy,所以补充了.
如果不是这样,别借鉴
x^2-xy=21,xy-y^2=-12
x^2-y^2=（x^2-xy）+(xy-y^2)=21+(-12)=9
x^2-2xy+y^2=(x^2-xy)-(xy-y^2)=21-(-12)=33

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