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Math Help - Integral

  1. #1
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    Unhappy Integral

    Integral ((e^x)*(1-(e^2x))^1/2 dx

    How can I solve this one. I don't know how to start it.

    Thank you
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  2. #2
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    \int \sqrt{e^x(1-e^{2x})} \delta x

    I'm still learning this myself, but I'm fairly sure that you would do this using substitution. I'm not suggesting that this is the best way to solve it, but note how using z=e^x alters the question:

    \int \sqrt{z (1-2z)} \delta x

    \int \sqrt{z - 2z^2} \delta x


    Perhaps you'll be able to solve it from here?
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  3. #3
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by noppawit View Post
    Integral ((e^x)*(1-(e^2x))^1/2 dx

    How can I solve this one. I don't know how to start it.

    Thank you
    are you sure you don't mean \int e^x \sqrt{1 - e^{2x}}~dx ?

    if that is the case, begin with a substitution of u = e^x. this yields the integral

    \int \sqrt{1 - u^2}~du

    the conventional way to deal with this latter integral is to use trig substitution, that is, substitute u = \sin \theta
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  4. #4
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    Quote Originally Posted by kwah View Post
    \int \sqrt{e^x(1-e^{2x})} \delta x

    I'm still learning this myself, but I'm fairly sure that you would do this using substitution. I'm not suggesting that this is the best way to solve it, but note how using z=e^x alters the question:

    \int \sqrt{z (1-2z)} \delta x

    \int \sqrt{z - 2z^2} \delta x


    Perhaps you'll be able to solve it from here?
    If  e^x = z, then e^{2x} = z^2.

    I suggest you combine the terms and then take e^{2x} as a common factor and take it out. Then use a substitution that will get rid of the e^x outside, and use another (trigonometric) substitution to solve. This way isn't pretty and I'm trying to find another easier way.

    EDIT: @Jhevon: he did pepper it with parentheses, so I don't think there is an ambiguity here: the e^x is in the square root.

    EDIT2: See ya!
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  5. #5
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Chop Suey View Post
    If  e^x = z, then e^{2x} = z^2.

    I suggest you combine the terms and then take e^{2x} as a common factor and take it out. Then use a substitution that will get ride of the e^x out, and use another (trigonometric) substitution to solve. This way isn't pretty and I'm trying to find another easier way.
    yup,. really ugly. that's why i'm hoping the poster made a mistake in typing the question ...oh! i gotta go to German class!
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  6. #6
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    Quote Originally Posted by noppawit View Post
    Integral ((e^x)*(1-(e^2x))^1/2 dx

    How can I solve this one. I don't know how to start it.

    Thank you
    As someone else has already pointed out, you are a mismatched brackets leaving this ambiguous, do you mean:

    \int e^x \sqrt{1-e^{2x}}\ dx

    or:

    \int \sqrt{e^x (1-e^{2x})}\ dx

    RonL
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  7. #7
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    I meant this \int e^x \sqrt{1-e^{2x}}\ dx actually.
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  8. #8
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    Then sub u = e^{x} and use another trig sub u = \sin{\theta}.
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  9. #9
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Chop Suey View Post
    EDIT: @Jhevon: he did pepper it with parentheses, so I don't think there is an ambiguity here: the e^x is in the square root.
    Quote Originally Posted by noppawit View Post
    I meant this \int e^x \sqrt{1-e^{2x}}\ dx actually.
    told ya

    had a lot of pepper, but not enough salt maybe
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