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Math Help - How do I go about evaluating this integral problem?

  1. #1
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    How do I go about evaluating this integral problem?

    let (sigma notation) [5, 14] f(x)dx=1, [5,8] f(x)dx=10, [11,14] f(x)=8
    Find [8, 11] f(x)dx
    and [11, 8] f(x)dx

    We went over the rules of computing integrals in class, but I don't see how that helps with this problem.
    Last edited by rhcprule3; November 18th 2013 at 04:23 PM.
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  2. #2
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    Re: How do I go about evaluating this integral problem?

    Hey rhcpule3.

    For your problem you have conflicting descriptions of your interval: Do you mean that [5,14] \ [5,8] OR [11,14] has f(x)dx = 1 (in other words any part of [5,14] that is also not in [5,8] or [11,14] has f(x)dx = 1)?
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  3. #3
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    Re: How do I go about evaluating this integral problem?

    let 14Σ5 f(x)dx=1, 8Σ5 f(x)dx=10, 14Σ11 f(x)=8
    Find 11Σ8 f(x)dx
    and 8Σ11 f(x)dx

    Sorry it took me a bit to figure out how to type sigma notation
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  4. #4
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    Re: How do I go about evaluating this integral problem?

    With that "dx" I think you must mean an integral rather than a sum (sigma).

    You are given that \int_5^{14} f(x)dx= 1, that \int_5^{8} f(x)dx= 10, that \int_{11}^{14} f(x)= 8.

    You want to find \int_8^{11} f(x)dx and \int_{11}^8 f(x)dx.

    One of the "rules of computing intervals" is that \int_a^b f(x) dx+ \int_b^c f(x)dx= \int_a^c f(x)dx which means that
    \int_5^8 f(x)dx+ \int_8^{11} f(x)dx= \int_5^11 f(x)dx and
    \int_5^{11} f(x)dx+ \int_{11}^{14} f(x)dx= \int_5^{14} f(x)dx.

    Putting in the information given those become
    10+ \int_8^{11} f(x) dx= \int_5^{11} f(x)dx and
    \int_5^{11} f(x)dx+ 8= 1

    Can you solve 10+ x= y and y+ 8= 1 for x?
    Last edited by HallsofIvy; November 19th 2013 at 05:33 AM.
    Thanks from rhcprule3
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  5. #5
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    Re: How do I go about evaluating this integral problem?

    Thanks, buddy! Much appreciated!
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