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  1. #61
    Colster's Avatar Contributor
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    Calculate this and get a FullInfoAccount
    the problem is you have to take the integral from the f(x) intersection to 1.

    A(square) = 1*1 = 1
    A(square)/2 = 0.5
    x interception = z

    integral{x0to[1]}(f(x)) = 0.5
    [x*ln(x)-x+a*x] {x0to[1]} = 0,5


    1*ln(1)-1+a*1 - [x0*ln(x0)-x0+a*x0] = 0.5 --> equation 1

    ln(x0) + a = 0
    ln(x0) = -a
    x0 = e^(-a)

    x0 -> equation 1

    -1 + a - (e^(-a))*ln(e^(-a)) + e^(-a) - a*e^(-a) = 0,5 |+1
    a + a*e^(-a)) + e^(-a) - a*e^(-a) = 1,5
    a + ( e^-a) = 1,5

    solution 1: 1.198290437
    solution 2: -.8576766739

    2 doesnt make any sense, so its

    test:

    f(x) = ln(x) + 1.198290437
    x0 = e^(-1.198290437) = .3017095628

    integral from .3017095628 to 1 f(x) = 0.5

    problem solved, its 1.198290437

    edit: so camicio is right, just wanted to solve the problem, i like mathematics (flames inc )
    Last edited by Colster; 03-12-2009 at 07:51 AM.

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  2. #62
    Ahskrew's Avatar Member
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    Ah, i now see what i did wrong, haha. ty Colster

  3. #63
    blubb12345's Avatar Contributor
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    Originally Posted by Ahskrew View Post
    a = 1.2344720351728634183955884763908
    okey, edited now, my guess is on this one

    WAA YOU ARE THE WINN0R

    1.2344720351728634183955884763908

    Last edited by blubb12345; 03-12-2009 at 03:06 PM.
    $50 SUBWAY CARD GIVEAWAY >> https://bit.ly/aMbaU5 << LIMITED TIME OFFER

  4. #64
    guitargod218's Avatar Banned
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    The answer is definitely over 9000 (never mind, it was answered already hehe).

    I'm a high school sophomore, and I'm very interested in how this problem is solved. However, I don't think I've ever been taught how to solve this (I'm in the equivalent of AP Algebra II this year and am going into AP Pre-calculus next year). Is this a calculus problem?

  5. #65
    wowpew's Avatar Active Member
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    What was wrong with my answer: a = -ln(x)+x ?

  6. #66
    Dendra's Avatar Active Member
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    Ah I didn't see this...I could have done it lol.
    The maths isn't that hard, it just requires a bit of thinking to work out what equations to solve

  7. #67
    ReidE96's Avatar Archer Authenticator enabled
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    Originally Posted by blubb12345 View Post
    Originally Posted by ReidE96
    wrong :P (integral of ln(X) is x*ln(x)-x (x>0))

    |||||||||
    vvvvvvvv
    Integral of f(x) = integral of ln(x) + ax +c
    =xlnx + ax + c - integral of 1
    =xlnx +(a-1)x + c
    i am sorry, its wrong
    and the rest is also wrong
    Actually, no, that bit isn't wrong. f(x) = ln(x) + a.
    integral ( f(x) )
    = integral ( ln(x) + a )
    = integral ( ln(x) ) + ax + c

    Using integral uv' = uv - integral vu',
    integral ln(x)
    = xln(x) - integral 1
    = xln(x) - x

    Hence,
    integral ( ln(x) ) + ax + c
    = xln(x) - x + ax + c
    = xln(x) + (a-1)x + c

    And it's what I said! Whay!

    (yes, I know it's been solved)

  8. #68
    camicio's Avatar Banned
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    Lol, you're right blubb12345. Do more giveaways like this please, I'll solve the next one hopefully .
    guitargod218 you just need to know how to integrate logarithms, know what an integral is and avoid doing stupid errors or making stupid assumptions.
    tamen, a is supposed to be a real constant number.

  9. #69
    Ahskrew's Avatar Member
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    Think this one was the hardes math problem ive ever solved tbh, haha and i got a account out of it sweet and ty

  10. #70
    blubb12345's Avatar Contributor
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    Originally Posted by ReidE96 View Post
    Actually, no, that bit isn't wrong. f(x) = ln(x) + a.
    integral ( f(x) )
    = integral ( ln(x) + a )
    = integral ( ln(x) ) + ax + c

    Using integral uv' = uv - integral vu',
    integral ln(x)
    = xln(x) - integral 1
    = xln(x) - x

    Hence,
    integral ( ln(x) ) + ax + c
    = xln(x) - x + ax + c
    = xln(x) + (a-1)x + c

    And it's what I said! Whay!

    (yes, I know it's been solved)

    uh sry missed the

    =xlnx + ax + c - integral of 1

    saw that the -x missed



    your mistake is that you chose the wrong upper limit for the integral

    the upper limit is where f(x)=1 but you chose 1 but thats wrong so it becomes wrong where you equalize
    F(x0)-F(1)=0.5
    it should be
    F(x0)-F(x1)+1-x1=0,5
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  11. #71
    Szharz's Avatar Contributor
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    X= over 9000!!!! Gief account nao den!! Pliiiiiiiz



  12. #72
    ReidE96's Avatar Archer Authenticator enabled
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    Ah, of course, that would be it. Thanks, blubb. It annoys me if I get something wrong and can't figure out where it went balls up. Not that I ever really intend on going back over it, I just like to know XD

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