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# Core 4 binomial expansion Q watch

1. From AQA MPC4 Jun 13

Question is attached; I have no idea how to do the last part of the Q

Any guidance is very much appreciated, thanks
2. What happens when x = 1/6 ?
3. We want to use our expansion to approximate the cube root. So we plug x=1/6 into the expansion as this makes the denominator 28.
However we need 2 lots of this so we multiply the expansion in bi) by 2. Then just use a calculator to give the answer to 6dp.
Just say if you need any more help cos I don't think I have explained this too well.
4. (Original post by EricPiphany)
What happens when x = 1/6 ?
(Original post by B_9710)
We want to use our expansion to approximate the cube root. So we plug x=1/6 into the expansion as this makes the denominator 28.
However we need 2 lots of this so we multiply the expansion in bi) by 2. Then just use a calculator to give the answer to 6dp.
Just say if you need any more help cos I don't think I have explained this too well.

?
5. (Original post by hi-zen-berg)

?
Becuase when subbed into (27+6x)^{-1/3} it gives us yummy yummy which we need
6. Let 27+6x=28
7. You want the denominator to be 28 so that you have cube root of 28 on denominator. So 27+6x=28
So x=1/6 so you sub that value into your expansion.
8. (Original post by B_9710)
You want the denominator to be 28 so that you have cube root of 28 on denominator. So 27+6x=28
So x=1/6 so you sub that value into your expansion.
Thanks
9. (Original post by EricPiphany)
Let 27+6x=28
(Original post by B_9710)
You want the denominator to be 28 so that you have cube root of 28 on denominator. So 27+6x=28
So x=1/6 so you sub that value into your expansion.
ahhhh i see

thanks guys, big help

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