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Math Help - Calculus substitution

  1. #1
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    Calculus substitution

    Alright I have a review questions I need help on for this upcoming test. So any help will greatly be appreciated and I'm sure provide to me getting an A on my next test which I surely need.

    Show that one of the substitutions u = e^3x, v = x-3, w= cos(3x) can be used to find an explicit antiderivative of x*sqrt(x-3). Find an explicted expression for integral x*(x-3) dx.

    Again thanks.
    Last edited by UMStudent; April 30th 2007 at 08:48 PM.
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  2. #2
    Senior Member ecMathGeek's Avatar
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    Quote Originally Posted by UMStudent View Post
    Alright I have a review questions I need help on for this upcoming test. So any help will greatly be appreciated and I'm sure provide to me getting an A on my next test which I surely need.

    Show that one of the substitutions u = e^3x, v = x-3, w= cos(3x) can be used to find an explicit antiderivative of x*sqrt(x-3). Find an explicted expression for integral x*(x-3) dx.

    Again thanks.
    It appears to me the u and w substitutions won't do you much good (u might, but it seems a bit too complicated to try). The v substitution is the obvious one to work.

    INT x*sqrt(x - 3) dx

    Let v = x - 3 --> x = v + 3 <--> dx = dv

    INT (v + 3)*sqrt(v) dv
    = INT v*sqrt(v) + 3*sqrt(v) dv
    = INT v^(3/2) + 3v^(1/2) dv
    = 2/5*v^(5/2) + 2v^(3/2) + C

    As for your second problem, x*(x-3) dx, no substitution is needed. Check to make sure this is the correct problem.
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  3. #3
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by ecMathGeek View Post

    As for your second problem, x*(x-3) dx, no substitution is needed. Check to make sure this is the correct problem.
    i think he was refering to the same question, x*sqrt(x - 3), in which case you already answered the question
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  4. #4
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    Yes the x*x-3 was just a typo I left out the sqrt. Thanks for your help and yes I did erase the first problem found i similiar problem I as able to work with.
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