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    #2
    On the last integral, is the upper bound "9"?

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    #3 Thread Author
    Quote Originally Posted by Rido12 View Post
    On the last integral, is the upper bound "9"?
    Yes.

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    #4
    Hello and welcome to MHB!

    Can you tell us what you've tried or what your thoughts are on how to begin, so our helpers have an idea where you are stuck and then can provide better help?

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    Quote Originally Posted by MarkFL View Post
    Hello and welcome to MHB!

    Can you tell us what you've tried or what your thoughts are on how to begin, so our helpers have an idea where you are stuck and then can provide better help?
    Thank you so much!
    I began with the condition that the secant must lie above the curve at all points if the curve is concave upward but that seem to lead nowhere. I also tried to utilise the fact that the double derivative of f(X) will be positive but to no avail.
    Any help will be appreciated.

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    #6
    I think I would begin with the minimal case:

    $ \displaystyle 0<f^{\prime\prime}(x)$

    So, integrating, what can you say about $f$?

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    Quote Originally Posted by MarkFL View Post
    I think I would begin with the minimal case:

    $ \displaystyle 0<f^{\prime\prime}(x)$

    So, integrating, what can you say about $f$?
    Wouldn't integrating this inequality conclude the same thing as what we are given, that f is a concave upward function?

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    #8
    Quote Originally Posted by mathisfun View Post
    Wouldn't integrating this inequality conclude the same thing as what we are given, that f is a concave upward function?
    What did you get when integrating?

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    #9 Thread Author
    Quote Originally Posted by MarkFL View Post
    What did you get when integrating?
    That f(x) is greater than zero, but that seems to be contradictory as a negative function may also have positive derivative.

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    #10
    Let's begin with:

    $ \displaystyle 0<f^{\prime\prime}(x)$

    And so, on $ \displaystyle [1,k]$ where $ \displaystyle 1<k\in\mathbb{R}$ there must be some constant $C$ such that:

    $ \displaystyle C<f^{\prime}(x)$

    What happens if you integrate again?

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