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Homework Help: Evaluate where F(x) is differentiable

  1. Mar 18, 2012 #1
    Hi there, I cannot seem to figure this question out.

    1. The problem statement, all variables and given/known data
    Let f: [0,3] -> R be defined as follows

    x if 0≤x<1,​
    f(X)= 1≤x<2
    x if 2≤x≤3​

    obtain formulas for F(x) = for 0≤x≤3 and sketch the graphs of f(x) and F(x). Where is F(x) differentiable? Evaluate F(x) where differentiable.

    I missed a day of class and am now totally lost. I've read through the sections in Intro to real analysis by Bartle that cover this section and I get no where. Any help on where to go would be greatly appreciated!
  2. jcsd
  3. Mar 18, 2012 #2


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    You are missing the definition of f(x) for x between 1 and 2.

    Hopefully, you know that f(x)= x is differentiable for all x. I suspect that the missing formula for x between 1 and 2 also defines a differentiable function. If that is the case, the only problem is whether the function is differentiable at the "joints", x= 1 and x= 2. Apply the definition of the derivative,
    [tex]\lim_{h\to 0}\frac{f(a+h)- f(a)}{h}[/tex]
    with a= 1 and then with a= 2. Look at the one sided limits.
  4. Mar 18, 2012 #3
    shoot. I missed that when I checked it over. it is f(x) = 1 if 1≤x<2

    With that information, would it really make much of a difference to what you said previously?
  5. Mar 18, 2012 #4


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    You have f(x) and F(x). What relationship is being assumed between those two functions?
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