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Homework Help: Trig Functions periodicity

  1. Feb 22, 2012 #1
    1. The problem statement, all variables and given/known data

    Basically, I had a test yesterday and one of the questions was:

    "an odd function f(x) has a period τ=7. What is the value of f(75)-f(-30)"

    2. Relevant equations


    3. The attempt at a solution

    I used periodicity to reduce

    = f(75-70) + f(30-28)
    = f(5) + f(2)

    What else could I have done?
  2. jcsd
  3. Feb 22, 2012 #2


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    Science Advisor
    Homework Helper

    welcome to pf!

    hi billy1024! welcome to pf! :smile:
    hint: what is the relation between f(5) and f(2) ? :wink:
  4. Feb 22, 2012 #3


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    Science Advisor

    since f is odd, f(-2) = -f(2), so f(2) = -f(-2).

    what is 5 - (-2)?
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