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# Edexcel C4 June 13R Watch

1. Very confused about how you get the answer to 4b, would be super grateful if someone could explain, thanks in advance
3. (Original post by sjmj24)
Very confused about how you get the answer to 4b, would be super grateful if someone could explain, thanks in advance
Set 8-9x = to 7100 and then solve for x.
Then substitute this value of x into your binomial expansion.
4. (Original post by khaleesi98)
Set 8-9x = to 7100 and then solve for x.
Then substitute this value of x into your binomial expansion.
that's what I tried but got completely different answer as they got x=0.1?
5. (Original post by sjmj24)
that's what I tried but got completely different answer as they got x=0.1?
Ooh that's worrying 😅 I'm having a look at the mark scheme now.

If anyone else wants to help it's on this paper...
http://qualifications.pearson.com/co...e_20130618.pdf
6. (Original post by sjmj24)
Very confused about how you get the answer to 4b, would be super grateful if someone could explain, thanks in advance
Let 8 - 9x = 7.1.

You know the cube root of 1000.

Does this help?
7. (Original post by ombtom)
Let 8 - 9x = 7.1.

You know the cube root of 1000.

Does this help?
Yeah that kinda makes sense now I see it, but what's wrong with what me and sjmj24 were going to do?

** Ooh is it that x would be too big???
8. (Original post by ombtom)
Let 8 - 9x = 7.1.

You know the cube root of 1000.

Does this help?
Ahh I see, I got confused as in the mark scheme they had it as 10 times the cube root of 71 maybe I missed a dot somewhere, thank you!
9. (Original post by khaleesi98)
Yeah that kinda makes sense now I see it, but what's wrong with what me and sjmj24 were going to do?

** Ooh is it that x would be too big???
Yep, the binomial expansion only works for "x" < 1 ("x" being the thing after "1 +").
10. (Original post by ombtom)
Yep, the binomial expansion only works for "x" < 1 ("x" being the thing after "1 +".
Ok. sjmj24 listen to him and not me haha x
11. Still both helpful as I understand it better now, if you're doing the C4 paper tomorrow good luck!

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