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    Substitution question

    (Q4 of Jan2013 edexcel C4)

    Anyway

    y= x/(1+ sqroot x)

    use u= 1 + sqr x

    soo what I did:

    rearraged some to get

    sqr x= u - 1
    x= (u - 1)^2

    and I got dx= 2(u-1)

    so

    integral of (u-1)^2/1+ (u-1) * 2(u-1) du

    cancelled the u-1 to get

    integral of 2(u-1)^2 du

    took the 2 out

    integrated (u -1)^2 and I got (u-1)^3 /(3)
    so

    2/3 (1 + sqr x)^3 + c



    where did I go wrong
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    TeeEm
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    You can't cancel the (u-1) because you have 1+ (u-1) on the denominator
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    (Original post by Student403)
    You can't cancel the (u-1) because you have 1+ (u-1) on the denominator


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    (Original post by Student403)
    You can't cancel the (u-1) because you have 1+ (u-1) on the denominator
    Oh lmao

    Thanks
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    (Original post by Dinaa)
    Oh lmao

    Thanks
    Sure
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    (Original post by Student403)
    You can't cancel the (u-1) because you have 1+ (u-1) on the denominator

    Question

    Is my dx ok?

    I know I could find du/dx, but instead I found dx/du and multiplied everything by du.
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    (Original post by Dinaa)
    Question

    Is my dx ok?

    I know I could find du/dx, but instead I found dx/du and multiplied everything by du.
    Yeah it's fine. I did the same and got 2(u-1)
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    You tried to integrate e^x and everyone knows e^x doesn't like to integrate.
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    (Original post by Awesome Genius)
    You tried to integrate e^x and everyone knows e^x doesn't like to integrate.


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    (Original post by Student403)


    So there's this function party going on and all of the hippest functions are there having a good time. Cos(x) is getting down and dirty with ln(x), 10^x is making the moves on the (x - 2)^2 twins and even x! dragged himself out for a good time.Unfortunately, one little function just wasn't having her night. e^x was sitting in a chair in the corner, tears dripping down exponentially. Sin(x) catches her out of the corner of his eye and decides to cheer her up. "Come on e^x! There's no reason to sit all on your lonesome crying. Get out into the crowd and have some fun. You know, INTEGRATE a little bit."e^x looks at Sin(x) with the saddest eyes and exclaims, "But it won't make any difference!"
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    (Original post by Awesome Genius)
    So there's this function party going on and all of the hippest functions are there having a good time. Cos(x) is getting down and dirty with ln(x), 10^x is making the moves on the (x - 2)^2 twins and even x! dragged himself out for a good time.Unfortunately, one little function just wasn't having her night. e^x was sitting in a chair in the corner, tears dripping down exponentially. Sin(x) catches her out of the corner of his eye and decides to cheer her up. "Come on e^x! There's no reason to sit all on your lonesome crying. Get out into the crowd and have some fun. You know, INTEGRATE a little bit."e^x looks at Sin(x) with the saddest eyes and exclaims, "But it won't make any difference!"
    :rofl:
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    (Original post by Awesome Genius)
    You tried to integrate e^x and everyone knows e^x doesn't like to integrate.
    no not really, e^x integrates to e^x

    its lnx that doesn't like integrating :unimpressed:
    Spoiler:
    Show
    well it does if you use integration by parts ( *1) and make u lnx.. but shh
 
 
 
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