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Binomial expansion help Watch

1. Hey guys,
Sorry for the unclear picture (this is June 13 AQA c4 question 3), but could anyone explain this to me?

I can get an correct expansion, I just don't understand why to find x there is a need to say 28^1/3 = 2*(27+6x)^-1/3 ?
2. (Original post by Serine)
Hey guys,
Sorry for the unclear picture (this is June 13 AQA c4 question 3), but could anyone explain this to me?

I can get an correct expansion, I just don't understand why to find x there is a need to say 28^1/3 = 2*(27+6x)^-1/3 ?
your trying to get this bracket (27+6x)^-1/3 to be 28 by inspection you can see if you let x be 1/6 youll be clear to proceed
3. (Original post by Sniperdon227)
your trying to get this bracket (27+6x)^-1/3 to be 28 by inspection you can see if you let x be 1/6 youll be clear to proceed
Thanks for responding - but I still don't understand this. Could you simplify your explanation further for me?

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Updated: June 7, 2016
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