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Math Help - Integration & Exponential Function

  1. #1
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    Integration & Exponential Function

    I am trying to solve the integral, lower limit 0 and upper limit 1, x * e^(-x^2) but I am slightly confused.

    Using a "u" substitution where u = -x^2, then du = -2xdx ... -du/2 = xdx.

    So the integral becomes, e^u * -du/2.

    I pull out the -1/2 constant in front of the integral and then integrate e^u * du.

    This becomes -1/2 * (e^u). Then using the Fundamental Theorem, F(b) - F(a), I have: -1/2 * [ e^(-1^2) - e^(-0^2) ]

    My answer is: -e/2 - 1/2

    Could someone tell me if my answer is correct and if not, where I went wrong? Thanks!
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  2. #2
    Junior Member mathemanyak's Avatar
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    re:

    let e^(-x^2)=u then -2x.e^(-x^2)dx=du
    then -1/2 int(x.e^(-x^2)dx)=-1/2int(du)=(-1/2).u=(-1/2)e^(-x^2)
    when go 1=> (-1/2)e^(-x^2)=(-1/2)e and when go 0=>(-1/2)e^(-x^2)=-1/2
    substraction them and get (-1/2)(e+1)
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