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    What is it? Im trying to do a volume generated around an axis question and Im not sure if Ive got the integral right..
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    cos4x = 1 - 2*[sin(2x)]^2
    [sin(2x)]^2 = [1-cos(4x)]/2
    integral = x/2 - [sin(4x)]/8
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    (Original post by Bezza)
    cos4x = 1 - 2*[sin(2x)]^2
    [sin(2x)]^2 = [1-cos(4x)]/2
    integral = x/2 - [sin(4x)]/8
    That was quick!!! :eek:
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    (Original post by Silly Sally)
    That was quick!!! :eek:
    I can't help it
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    (Original post by Bezza)
    cos4x = 1 - 2*[sin(2x)]^2
    [sin(2x)]^2 = [1-cos(4x)]/2
    integral = x/2 - [sin(4x)]/8
    This is wrong
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    (Original post by imasillynarb)
    This is wrong
    No it isn't, i just tried it and got exactly the same ans. I mean we could both be wrong but the chances prett slim me thinks!!!
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    (Original post by imasillynarb)
    This is wrong
    Care to elaborate? (Try differentiating it, www.calc101.com if you want)
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    (Original post by Silly Sally)
    No it isn't, i just tried it and got exactly the same ans. I mean we could both be wrong but the chances prett slim me thinks!!!
    It doesnt give me the right answer for the volume generated, so it must be
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    (Original post by imasillynarb)
    It doesnt give me the right answer for the volume generated, so it must be
    Well - just to make sure, does (sin2x)^2= 1/2(1 - cos4x)
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    Ooops, wait a minute, it does work, I didnt read the x/2 at first!! silly me
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    You haven't forgotten to square the whole thing have you? The curve may be (sin2x)^2?
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    (Original post by imasillynarb)
    It doesnt give me the right answer for the volume generated, so it must be
    What's the full question?

    Sally - yes it does, my earlier link is a good place for checking integration/differentiation and it gives the same answer as us
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    (Original post by imasillynarb)
    Ooops, wait a minute, it does work, I didnt read the x/2 at first!! silly me
    :rolleyes:
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    (Original post by Bezza)
    What's the full question?

    Sally - yes it does, my earlier link is a good place for checking integration/differentiation and it gives the same answer as us
    All sorted now!!!
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    While on the subject of integration - can someone tell me whether it is possible to integrate:

    e^(x^2)

    I know we can differentiate it, but when integrating it, would the ans be:

    1/x(e^(x^2))

    Thanks
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    (Original post by Silly Sally)
    While on the subject of integration - can someone tell me whether it is possible to integrate:

    e^(x^2)

    I know we can differentiate it, but when integrating it, would the ans be:

    1/x(e^(x^2))

    Thanks
    I'm pretty sure you can't integrate it, no.

    Try differentiating what you have using the quotient rule - u = e^x^2, v = x
    dy/dx = (vu' - uv')/v^2 = (x*2x*e^x^2 - e^x^2)/x^2 = e^x^2(2x^2 - 1)/x^2
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    (Original post by Bezza)
    I'm pretty sure you can't integrate it, no.

    Try differentiating what you have using the quotient rule - u = e^x^2, v = x
    dy/dx = (vu' - uv')/v^2 = (x*2x*e^x^2 - e^x^2)/x^2 = e^x^2(2x^2 - 1)/x^2
    Well as long as i know i don't have to integrate it - then i am happy

    I ALWAYS do this, i always wonder what would happen if a particular question is on the exam, then when i can't do it i begin to worry!!!

    One of the reasons i am "silly" sally!!!
 
 
 
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