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<<Integral depending on parameter >>?

Evaluate integral J(x,p) = [0, 1] ∫ [atan(p*x)] /[x*√(1-x²)] dx using differentiation by parameter.

Update:

Oops, sorry, of course it is J(p). It was given to me like that but it is wrong...

Update 2:

Yes, you are right Alpha, I just don't understand why you left that a, because it was atan = arctan and you differentiated it as arctangent but left a .

3 Answers

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  • 1 decade ago
    Favorite Answer

    dJ(p)/dp=[0, 1] ∫x/(1+(px)^2)*(x*√(1-x²))dx

    =[0, 1] ∫1/(1+(px)^2)*(√(1-x²))dx

    =∫1/(1+(px)^2)*(√(1-x²))dx

    x=sin(k)

    dx=cos(k)

    =∫1/1+(p^2)(sink)^2

    =∫(coseck)^2/(coseck)^2+p^2

    =∫(coseck)^2/(cotk)^2+p^2+1

    cotk=t

    -(coseck)^2dk=dt

    =-∫1/t^2+y^2

    where y=sqrt(1+p^2)

    -1/yarctan(t/y)

    =(-1/sqrt(p^2+1))arctan(t/sqrt(1+p^2))

    =(-1/sqrt(p^2+1))arctan((1/x)sqrt((1-x^2)/(1+p^2)))

    http://integrals.wolfram.com/index.jsp?expr=1%2F%2...

    from 0 to 1 it becomes

    pi/(2sqrt(1+p^2))

    dJ(p)/dp=pi/(2sqrt(1+p^2))

    integrating w.r.t p both sides of equation

    J(p)=(pi/2)∫sqrt(1+p^2)

    p=tanz

    and doing integration

    i got the answer to be

    (pi/2) ln|sqrt(1+p^2)+p|

    am i correct.

    sorry,in the beginning i did it as arctan but at the end i just forgot it and took 'a' as a const

  • ?
    Lv 4
    4 years ago

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  • DavidG
    Lv 5
    1 decade ago

    hey Rasa,

    J(x,p) ??... is the integral expression not with respect to 'x' ??, how can 'x' be an independent variable of J(x,p) ??

    David

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