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Relating to period of a function.

  1. May 1, 2013 #1
    If we have f(k)=Asin([itex]\frac{xa}{2}[/itex]). Then it was mentioned that f(x) is a periodic function with period [itex]\frac{Δx.a}{2}[/itex]=π. How come?

    Thanks!

    Please note, A and a are constants.
     
  2. jcsd
  3. May 1, 2013 #2

    Mark44

    Staff: Mentor

    This should be f(x) = A sin(##\frac{xa}{2}##). The only variable here is x. k doesn't appear at all in the formula for this function.
    This is wrong, and I have no idea where you got this.

    The sine and cosine functions are periodic. The period of both sin(x) and cos(x) is 2##\pi##. The period of sin(Kx) and cos(Kx) is ##\frac{2 \pi}{K}##.

    What then would be the period of sin((a/2)x)?
     
  4. May 1, 2013 #3
    Sorry it is x, I typed it by mistake. It should be 4π/a. But here they related the variable of the sin function "x" to the period in some way I didn't understand.. (i.e, the formula that I wrote in my first post and that you quoted second).
    Thanks
     
  5. May 1, 2013 #4

    Mark44

    Staff: Mentor

    If the period of sin(Kx) is ##2\pi/K##, what is the period of sin((a/2)x)?
     
  6. May 1, 2013 #5
    I answered you previously, it would be 4π/a
     
  7. May 1, 2013 #6

    Mark44

    Staff: Mentor

    You said it "should be 4π/a", which I interpreted to mean that you knew that was the answer, but didn't know how it was obtained.

    You asked about the formula in your first post (and that I quoted). I have no idea what they mean by that formula, especially the part with Δx.
     
  8. May 1, 2013 #7
    Yes. Neither do I. Thank you anyway!
     
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