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Homework Help: Find period of function

  1. Aug 20, 2008 #1
    f(x) = - sin(x/5 - pi)

    the period for this is -pi correct, since, k taken out it is 1, and by divide -pi into 1, the answer will be -pi only, correct??
     
  2. jcsd
  3. Aug 20, 2008 #2

    mgb_phys

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    Re: Period

    I don't think you can have a negative period!
    To find the period pick a value of x (say zero) and then work out what is the next value of x that will give the same value of f().
    Does adding the same constant to both values of X do anything?
     
  4. Aug 20, 2008 #3
    Re: Period

    Does it gives the same pi??
     
  5. Aug 20, 2008 #4
    Re: Period

    So, the answer is "pi"??
     
  6. Aug 20, 2008 #5

    mgb_phys

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    Re: Period

    The period of sin() is pi ie sin(0)=sin(pi)

    But in terms of X, since you divide X by 2 what value of X do you need for the function to give the same value as for x=0?
     
  7. Aug 20, 2008 #6
    Re: Period

    What is the exact period of f(x) (in radians)? (Recall p radians is equivalent to 180°; p is obtained by entering: Pi or pi.)

    What does the question actually wants anyway?? how to calculate period in radians.
     
  8. Aug 20, 2008 #7
    Re: Period

    zero??
     
  9. Aug 20, 2008 #8

    Avodyne

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    Re: Period

    This is not correct. A function [itex]f(x)[/itex] is periodic with period [itex]p[/itex] if
    [tex]f(x+p)=f(x)[/tex]
    for all real [itex]x[/itex]. For [itex]\sin(x)[/itex], this is true for [itex]p=2\pi[/itex], and not true for [itex]p=\pi[/itex], because [itex]\sin(x+\pi)=-\sin(x)[/itex], not [itex]\sin(x)[/itex].
     
  10. Aug 20, 2008 #9
    Re: Period

    yes, and the answer is 10pi, by getting the 2pi divide 1/5 to get the answer. I get confuse that i need to multiply by 5 so to get b=5, but when i try 1/5, it's done.
     
  11. Aug 20, 2008 #10

    Avodyne

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    Re: Period

    Correct!
     
  12. Aug 20, 2008 #11

    Astronuc

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    Re: Period

    in this function, f(x) = - sin(x/5 - pi), the -pi would be a phase shift.

    In general for sin (wt + q), w = 2pi f = 2 pi/T, where T is the period, and q is the phase shift.
     
  13. Aug 21, 2008 #12

    HallsofIvy

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    Re: Period

    No, the period of sin(x) is 2pi.

    fr33pl4gu3. your function is -sin(x/5- pi). When x/5- pi= 0, what is x? When x/5- pi= 2pi, what is x? The difference between those is the period.
     
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