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Math Help - finding roots in given interval /differentiation

  1. #1
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    finding roots in given interval /differentiation

    p
    Last edited by philyc86; November 7th 2008 at 07:29 AM.
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by philyc86 View Post
    hi there
    can anyone point me in the right direction about how to show that the following equation has a root in the interval [1.1 , 1.2]

    2x-tanx=0
    2x-tan(x) is positive at x=1.1 and negative at x=1.2 and as it is continuous on this interval it has a root in the interval.

    CB
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  3. #3
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    Quote Originally Posted by philyc86 View Post
    also ,how do i differentiate (x-1)lnx ,i need to find the 2,3,4,and 5th derivative ,and i get stuck as to wheher to use the product or quotient rules and how to deal with some of the powers

    thankyou so much

    phil
    They are essentially the same thing so use which ever is the more convienient, remember that:

    \frac{f(x)}{g(x)}=f(x) \left( \frac{1}{g(x)}\right)

    and that \frac{d}{dx}\left(\frac{1}{g(x)}\right)=-\ \frac{g'(x)}{(g(x))^2}

    CB
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    p
    Last edited by philyc86; November 7th 2008 at 07:30 AM.
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  5. #5
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    Quote Originally Posted by philyc86 View Post
    hi
    thanks for your reply
    regarding 2x-tanx =0 ,i get a positve answer with both 1.1 and 1.2 !What do you do in this situation ,for newton raphson dont you need to find a point where it changes from positive to negative .

    thankyou
    Check the angle mode of your calculator, it should be set to radians

    CB
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