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    • Thread Starter
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    Getting a bit deflated by this.......I can't even do the first question.......:facepalm:

    1a) Differentiate x (1+3x)^5

    I'm not going to go through each step, but using the product rule (and the chain rule to an extent), I got:

    (1+3x)^5 + 15x (1+3x)^4

    But the answer is (1+3x)^4 (1+18x)?

    Could anyone enlighten me as to where I've gone wrong?
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    You haven't gone wrong, you just haven't simplified (or, rather, factorised) it. Take (1+3x)^4 out as a common factor.
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    (Original post by Introverted moron)
    Getting a bit deflated by this.......I can't even do the first question.......:facepalm:

    1a) Differentiate x (1+3x)^5

    I'm not going to go through each step, but using the product rule (and the chain rule to an extent), I got:

    (1+3x)^5 + 15x (1+3x)^4

    But the answer is (1+3x)^4 (1+18x)?

    Could anyone enlighten me as to where I've gone wrong?
    You're not wrong, you just need to go a step further and take out a common factor of (1+3x)^4 from each part of your expression and re-arrange the rest.

    Edit: Too slow :sigh:
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    Generally they like you to take out a common factor, in this case from your answer it would be (1+3x)^4.

    EDIT: Even slower :P
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    (Original post by Introverted moron)
    Getting a bit deflated by this.......I can't even do the first question.......:facepalm:

    1a) Differentiate x (1+3x)^5

    I'm not going to go through each step, but using the product rule (and the chain rule to an extent), I got:

    (1+3x)^5 + 15x (1+3x)^4

    But the answer is (1+3x)^4 (1+18x)?

    Could anyone enlighten me as to where I've gone wrong?
    If you facctorise your answer you should get the same as the books answer.
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    Ah, I see. Thank you all.
 
 
 
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Updated: April 10, 2011
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