Question

（a-b）³=a³-3a²b+3ab²-b³是怎么算的

（a-b）³=a³-3a²b+3ab²-b³是怎么算的中间为什么会变成+的

Answer 1

(a-b)平方 ×(a-b)=(a平方-2ab+b平方)×(a-b)

(剩下自己化）就能得到题目上那个式子。

追答

（a-b）³

=(a-b)²(a-b)
=(a²-2ab+b²)(a-b)
=a³-2a²b+ab²-a²b+2ab²-b³
=a³-3a²b+3ab²-b³

Answer 2

（a-b）³
=(a-b)²(a-b)
=(a²-2ab+b²)(a-b)
=a³-2a²b+ab²-a²b+2ab²-b³
=a³-3a²b+3ab²-b³

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