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Thread: Mean Value Theorem

  1. #1
    Junior Member
    Dec 2008

    Mean Value Theorem

    Using the Mean Value Theorem, prove that ln(103) - ln(100) is less than or equal to 0.03

    I tried taking f(x) = 1/x on the interval [100,103]. The average value would then be (1/3)[ln(103)-ln(100)].

    I don't know how to proceed after this or even if I'm on the right track.
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  2. #2
    Math Engineering Student
    Krizalid's Avatar
    Mar 2007
    Santiago, Chile
    Well, you actually gotta take $\displaystyle f(x)=\ln x$ then exists $\displaystyle c\in(100,103)$ so that $\displaystyle \frac{\ln 103-\ln 100}{3}=\frac{1}{c}.$

    On the other hand is $\displaystyle 100<c<103$ so $\displaystyle \frac1{103}<\frac1c<\frac1{100}$ and then $\displaystyle \frac{1}{103}<\frac{\ln 103-\ln 100}{3}<\frac{1}{100},$ so pick the second inequality and $\displaystyle \ln 103-\ln 100<\frac{3}{100}=0,03.$
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