已知x² -xy= 21 xy-y²=-12.则代数式x²-y²=?x²-2xy+y²=?
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已知x² -xy= 21 xy-y²=-12.则代数式x²-y²=?x²-2xy+y²=?
已知x² -xy= 21 xy-y²=-12.则代数式x²-y²=?x²-2xy+y²=?
已知x² -xy= 21 xy-y²=-12.则代数式x²-y²=?x²-2xy+y²=?
(x^2-xy)+(xy-y^2)=x^2-y^2=21-12=9
(x^2-xy)-(xy-y^2)=x^2-2xy+y^2=21-(-12)=21+12=33
x²-y²=x² -xy+xy-y²=21-12=9
x²-2xy+y²=x² -xy-(xy-y²)=21+12=33
12
第一个等式=9
第二个等式=33