1 (x^2-y^2)-(x-y)^22 3(x^2-27)-四分之三x^23 x^2n-9^n另外一题加5分

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1 (x^2-y^2)-(x-y)^22 3(x^2-27)-四分之三x^23 x^2n-9^n另外一题加5分
1 (x^2-y^2)-(x-y)^2
2 3(x^2-27)-四分之三x^2
3 x^2n-9^n
另外一题加5分

1 (x^2-y^2)-(x-y)^22 3(x^2-27)-四分之三x^23 x^2n-9^n另外一题加5分
1 (x^2-y^2)-(x-y)^2
=(x+y)(x-y)-(x-y)^2
=(x-y)[x+y-(x-y)]
=2y(x-y)
2 3(x^2-27)-3/4x^2
=3(x^2-27-1/4x^2)
=3(3/4x^2-27)
=3*3(1/4x^2-9)
=9(1/2x+3)(1/2x-3)
3 x^2n-9^n
=n(x^2-9)
=n(x+3)(x-3)

1 (x^2-y^2)-(x-y)^2=(x-y)（（x+y)-(x-y)）==2y(x-y)
2 3(x^2-27)-四分之三x^2=（(3/2)*X-9）（(3/2)*X+9）
3 x^2n-9^n=（x^n-3^n）=（x^n+3^n）
你是几年级了？这些很简单的，都是考你一个公式:（x^2-y^2）=(x-y）（X+Y）

考的是平方和公式，好好去书上看一下平方和和和平方的公式
呵呵楼上给的答案都对我就不再写了
这两个公式千万别搞混了是初一吧我上学那会也总是记差注意观察多做点题你就能看出来了

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