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Edexcel C4 June 13R

Very confused about how you get the answer to 4b, would be super grateful if someone could explain, thanks in advance
Link to question please?
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Avatar for sjmj24
sjmj24
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http://qualifications.pearson.com/content/dam/pdf/A%20Level/Mathematics/2013/Exam%20materials/6666_01R_que_20130618.pdf
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.
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sjmj24
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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?
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/content/dam/pdf/A%20Level/Mathematics/2013/Exam%20materials/6666_01R_que_20130618.pdf
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Avatar for ombtom
ombtom
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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? :tongue:
Original post by ombtom
Let 8 - 9x = 7.1.

You know the cube root of 1000.

Does this help? :tongue:


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???
(edited 7 years ago)
Reply 8
Avatar for sjmj24
sjmj24
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Original post by ombtom
Let 8 - 9x = 7.1.

You know the cube root of 1000.

Does this help? :tongue:


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!
Reply 9
Avatar for ombtom
ombtom
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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 +").
(edited 7 years ago)
Original post by ombtom
Yep, the binomial expansion only works for "x" < 1 ("x" being the thing after "1 +":wink:.


Ok. @sjmj24 listen to him and not me haha x
Reply 11
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sjmj24
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Still both helpful as I understand it better now, if you're doing the C4 paper tomorrow good luck! :smile:

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