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When I simplify $(3a-b^2-a)^3$, I used $(u±v)^3=u^3±3u^2v+3uv^2±v^3$

but I'm confused with $(b^2-a)$

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You should slow down and absorb the answers on your previous question before continuing to post questions of the same form. – Zev Chonoles Jul 14 '12 at 7:52
thanks for the advice sir Zev Chonoles – user12515 Jul 14 '12 at 8:04
up vote 1 down vote accepted

First of all, your cited identity is incorrect; the exponent on the $v$ was wrong in the last term. The correct version is $$(u\pm v)^3=u^3\pm 3u^2v + 3uv^2\pm v^3.$$ Also, note that $$3a-b^2-a=2a-b^2$$ so that $$(3a-b^2-a)^3=(2a-b^2)^3,$$ and you can then let $u=2a$ and $v=-b^2$, making the problem somewhat more straightforward.

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I guest I need a tutor Thanks sir – user12515 Jul 14 '12 at 8:05

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