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    xxzzy's Avatar
    xxzzy Posts: 4, Reputation: 1
    New Member
     
    #1

    Jan 15, 2008, 03:54 AM
    Integration using substitution
    Hi,
    I am attempting to solve an integration problem.

    x^2 Numerator
    (8 - 3x^2) Denominator.

    I would like to see the steps, as textbooks that I have consulted either avoid a question type like this or use various greek letters to show the steps but which are confusing. I realise that substitution must be used but surely this is after you take the lower line (8 - 3x^2) up to the top line and give it a negative power (-1). What then happens to the x^2 does it multiply into bracket (8 - 3x^2)?

    Grateful for help.
    Regards
    Sandy Forrester:( :(
    jiten55's Avatar
    jiten55 Posts: 105, Reputation: 8
    Junior Member
     
    #2

    Jan 15, 2008, 08:26 AM
    x^2/(8 - 3 x^2) = 1/3 [8/(8 - 3x^2) - 1]

    = A + B

    A = (8/3)/(8 - 3x^2), B = -1/3


    Integral of B = -1/3 x

    For integral of A,

    Use formula for Integral of 1/(a^2 - u^2)

    = (1/2a) log [(a + u)/(a - u) ]

    Without using formula, you can see:

    1/(a^2 - u^2) = (1/2a) [1/(a - u) + 1/ (a + u)]

    from which you can derive the formula.

    I hope the above is clear, if not let me know.

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