计算:(x-y+9)(x+y-9)

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计算:(x-y+9)(x+y-9)计算:(x-y+9)(x+y-9)计算:(x-y+9)(x+y-9)(x-y+9)(x+y-9)=[x-(y-9)][x+(y-9)]=x^2-(y-9)^2(x-y

计算:(x-y+9)(x+y-9)
计算:(x-y+9)(x+y-9)

计算:(x-y+9)(x+y-9)
(x-y+9)(x+y-9)
=[x-(y-9)][x+(y-9)]
=x^2-(y-9)^2

(x-y+9)(x+y-9)
=[x-(y-9)]*[x+(y-9)]
=x^2-(y-9)^2
=x^2-y^2+18y-81

x*x-y*y-81+18x

x^2-(y-9)^2

x^2-y^2-81

[x-(y-9)]*[x+(y-9)]
=x*x-(y-9)*(y-9)
=……
下面的自己算。。不会输平方号就是麻烦