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

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

已知x²-xy=21,xy-y²=-12,分别求式子x²-y²与x²-2xy+y²的值
x²-xy=21,
xy-y²=-12
二式相加得x²-y²=9
二式相减得x²-2xy+y²=33

已知x²-xy=21，xy-y²=-12，所以两式相加，得到x²-y²=9，两式相减，得到x²-2xy+y²=33

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)=33