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# C4 binomial expansion Watch

1. Not really understanding last part of this Q

Any help is greatly appreciated
2. You have to use the second part to do the third. What happens if you let x=1/3 in the 2nd expansion you got?
3. As said above. If x=1/3 then you have (from the second part of the question) .
4. (Original post by Ano9901whichone)
You have to use the second part to do the third. What happens if you let x=1/3 in the 2nd expansion you got?
(Original post by B_9710)
As said above. If x=1/3 then you have (from the second part of the question) .
okay i see. thanks

could someone explain why the 'second part' of the question can be used? i.e. the 8+3x inside brackets

what is not valid about (1+8)^1/3 = 9^1/3 ?
5. (Original post by hi-zen-berg)
okay i see. thanks

could someone explain why the 'second part' of the question can be used? i.e. the 8+3x inside brackets

what is not valid about (1+8)^1/3 = 9^1/3 ?
I'm sure you've learnt that the binomial expansion of for non-integer is only valid for . It should be written in your formula booklet as well, next to the expansion.

Sooo, can't really plug in .

On the other hand is valid for so is perfectly valid here.
6. (Original post by Zacken)
I'm sure you've learnt that the binomial expansion of for non-integer is only valid for . It should be written in your formula booklet as well, next to the expansion.

Sooo, can't really plug in .

On the other hand is valid for so is perfectly valid here.
Ahh I see thanks; have learnt that but it was a bit abstract and didn't care aha
7. (Original post by hi-zen-berg)
Ahh I see thanks; have learnt that but it was a bit abstract and didn't care aha
Basically always think about what restrictions apply when it comes to plugging things into expansions!

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