(x-y-3)(x-y+3)怎么做

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(x-y-3)(x-y+3)怎么做(x-y-3)(x-y+3)怎么做(x-y-3)(x-y+3)怎么做=(x-y)2-9=x2-2xy+y2-9其中2是平方的意思=(x-y)²-9=x

(x-y-3)(x-y+3)怎么做
(x-y-3)(x-y+3)怎么做

(x-y-3)(x-y+3)怎么做
=(x-y)2 - 9=x2-2xy+y2-9其中2是平方的意思

=(x-y)²-9
=x²-2xy+y²-9