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Math Help - integral of f*g product

  1. #1
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    integral of f*g product

    function f is integrable over [a,b]
    function g is integrable over [a,b]

    and g =
    { 1 on [a,b],
    0 otherwise }

    If I have  \int_a^b fg

    Can I treat g as a constant and write:

     \int_a^b fg = \int_a^b f
    Last edited by director; November 18th 2013 at 08:08 PM.
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  2. #2
    MHF Contributor
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    Re: integral of f*g product

    Hey director.

    The answer is yes: you can do exactly that if g(x) = 1 for x in [a,b].
    Thanks from director and HallsofIvy
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  3. #3
    MHF Contributor

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    Re: integral of f*g product

    Since you are integrating only from a to b, what happens outside that interval is irrelevant.

    In fact, if f were integrable on [p, q] with p< a< b< q, \int_p^q fg dx= \int_a^b f(x) dx.
    Thanks from director
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