已知x² -xy= 21 xy-y²=-12.则代数式x²-y²=?x²-2xy+y²=?

问题描述:

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