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Homework Help: Fundamental Period (graph)

  1. Nov 17, 2009 #1
    1. The problem statement, all variables and given/known data

    The elements of f(t) are 1+kt and t here are 0<t<1
    the other element is 1 and t here are 1<t<2.


    prove if k is not equal to zero, the period f is 2.

    i know the graph of element 1 but how should I graph the other element with k.
    Based from the graph, the period is 2.

    How should I prove that using mathematical statement?

    2. Relevant equations

    The problem is all about fundamental period
  2. jcsd
  3. Nov 17, 2009 #2


    Staff: Mentor

    What do you mean "elements of f(t)"?
    I don't have any idea of what you saying here:
    Are you saying that f(t) = 1 + kt, if 0 < t < 1, and f(t) = 1, if 1 < t < 2?
    Is f(t + 2) = f(t) given, or is that what you're trying to prove?
  4. Nov 17, 2009 #3
    thats what i am saying. f(t+2) =f(t) is given. what im trying to prove is that if k is not equal to zero, the period f is 2.
    how i should i plot the 1+kt?
    Last edited: Nov 17, 2009
  5. Nov 17, 2009 #4


    Staff: Mentor

    Well, you don't know k, other than it isn't zero, so you have a line segment with pos. slope if k > 0, and neg. slope if k < 0. It doesn't really matter whether it slopes up or down, just so long as the line isn't horizontal.
  6. Nov 17, 2009 #5
    ok so how I prove by mathematical statement that the period f is 2? can this be
    or it can only be proved by graph?
  7. Nov 17, 2009 #6


    Staff: Mentor

    A function is periodic with period p iff f(x + p) = f(x) for all x. (See the definition on this Wikipedia page: http://en.wikipedia.org/wiki/Periodic_function.)

    So the information that you tell me is given would seem to do the trick except when k = 0. In that case, f(x) = 1 at most points, which would imply that the period was smaller than 2. I say "at most points" because from the information in your post, f(x) is not defined at x = 0, x = 1, and x = 2.

    Are you sure you have posted the problem exactly the way it reads? It bothers me that f isn't defined at 0, 1, and 2, and it also bothers me that you are given that f(t + 2) = f(t), since that's essentially what you need to prove.
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