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Homework Help: General Phase Shift Question

  1. May 26, 2012 #1
    Find the phase shift of a function.

    Y=-5sin(x-pie/2)

    The Phase shift is (pie/2)/1 which equals to pie/2. The correct answer is units to the right though..which is where I need clarification on.

    My book said if phi is less than 0, it is too the left.. being -pie/2 wouldn't this indicate to the left?

    Another example.

    y=4cos(x+pie/2) once again phase shift is pie/2...but it is units to the left...units to left indicates phi...which is pie in this case..is negative...how is that possible?

    It is easy to remember if it has a plus sign..it is units to the left...
    negative sign ends up being units to the right...I just don't understand and if I don't truly understand than I won't remember it long term.

    Thanks for your help.





    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. May 26, 2012 #2

    SammyS

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    Does your book say something like:
    For
    [itex]\sin(x-\phi)\,,[/itex]​
    if [itex]\phi[/itex] is positive then the shift is to the right,

    if [itex]\phi[/itex] is negative then the shift is to the left .​

    ?

    If that's the case, then your [itex]\phi[/itex] is π/2, which is positive.
     
  4. May 26, 2012 #3
    ah, so they are factoring in that your equation sin(w-phi) can make two negatives into a positive...
     
  5. May 26, 2012 #4

    SammyS

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    Yes.
     
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