Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Questions Regarding Limits

  1. Aug 28, 2011 #1
    Have a couple of questions that I've been stuck with for some time. Would greatly appreciate the help. No idea how I should approach these questions and how do I start.

    6. Suppose that a function f is continuous on the closed interval [0,1]and that 0≤f(x)≤1 for every x in [0,1].Show that there must exist a number c in [0,1] such that f(c)=c(c is called a fixed point of f).

    (7) Is it true that if you stretch a rubber band by moving one end to the right and the other end to the left, some point of the band will end up in its original position? Give reasons for your answer.

    (8) Is there any reason to believe that there is always a pair of antipodal (diametrically opposite) points on Earth’s equator where the temperatures are the same? Explain.
  2. jcsd
  3. Aug 28, 2011 #2


    User Avatar
    Homework Helper

    Consider g(x) = f(x) - x. What property does this function have? Try to think what else you could do with g(x).
  4. Aug 28, 2011 #3
    From where do I derive the equation g(x)=f(x)-x?
  5. Aug 28, 2011 #4
    I reckon that I should perhaps use composite functions to do this but I have no idea from where can i get the function g(x) from.
  6. Aug 29, 2011 #5
    Managed to get both questions 6 and 7 down.

    Not sure whether my working for 7 is correct though.

    Let x1 be the new position of the left end of the elongated rubber band.
    let d(x) be the displacement from the original position.

    d(x) = x - x1 <0

    Let x2 be the new position of the right end of the elongated rubber band.
    d(x) = x2 - x >0

    Therefore by Intermediate Value Theorem, d(x) = 0 must exist. Hnece some part of the elongated rubber band must be at the oringal position.
  7. Aug 29, 2011 #6
    how do i go about question 8 though?

    I don't really get the question. Know that i must make use of intermediate value theorem somehow but i have no idea how i'm supposed to do it.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook