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    Hi really need some help with this FP1 question, unsure how to start it. Any hints or pointers would be much appreciated.

    Thanks in advance

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    Replace all occurrences of x with u+2. So x^3 becomes (u+2)^3 and so on, then expand out.
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    (Original post by Hopple)
    Replace all occurrences of x with u+2. So x^3 becomes (u+2)^3 and so on, then expand out.
    Unless I've expanded incorrectly, I keep ending up with X^3 -5 = 0

    No idea what to even do with that.

    Sorry, still really confused!
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    (Original post by freshypot♥)
    Unless I've expanded incorrectly, I keep ending up with u^3 -5 = 0

    No idea what to even do with that.

    Sorry, still really confused!
    Changed x to u. You really can't find a solution for u^3 = 5 ?
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    (Original post by Mr M)
    You really can't find a solution for x^3 = 5 ?
    No, I meant that because the questions asks for the exact real root of the equation, and the solutions for u^3 -5 = 0 are all real but not exact, it's not giving me the correct answer, so I must be doing something fundamentally wrong.

    I can find the solutions to u^3 = 5 though!
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    (Original post by freshypot♥)
    No, I meant that because the questions asks for the exact real root of the equation, and the solutions for x^3 -5 = 0 are all real but not exact, it's not giving me the correct answer, so I must be doing something fundamentally wrong.

    I can find the solutions to x^3 = 5 though!
    I don't think you know what exact means.

    u=\sqrt[3] 5 is exact. Stop changing u (incorrectly) to x!
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    (Original post by freshypot♥)
    Unless I've expanded incorrectly, I keep ending up with X^3 -5 = 0

    No idea what to even do with that.

    Sorry, still really confused!
    Do you get u^3-5=0? If so, find u's real root, then substitute back that u=x-2
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    (Original post by Mr M)
    I don't think you know what exact means.

    u=\sqrt[3] 5 is exact. Stop changing u (incorrectly) to x!
    Ooops, sorry! I entered it into my calculator, and it gave me a decimal answer, therefore I thought it couldn't be exact. Bit stupid really.

    So, my root answer would be \sqrt[3] 5 + 2 ?
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    (Original post by freshypot♥)
    Ooops, sorry! I entered it into my calculator, and it gave me a decimal answer, therefore I thought it couldn't be exact. Bit stupid really.

    So, my root answer would be \sqrt[3] 5 + 2 ?
    Yes.
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    (Original post by Mr M)
    Yes.
    Thanks!
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    (Original post by Hopple)
    Do you get u^3-5=0? If so, find u's real root, then substitute back that u=x-2
    Thanks for your help!
 
 
 
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