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Homework Help: Graphing sin and cos functions

  1. Sep 8, 2010 #1
    1. The problem statement, all variables and given/known data

    plot x(t) = 10cos((pi*t)-(pi/4))

    2. Relevant equations

    pi/4 is the shift to the right

    10 is the amplitude of the graph

    pi is the radian frequency

    3. The attempt at a solution

    so i got the amplitude and shift to the right by pi/4 part but as for the radian frequency, my plot doesnt seem right. does pi mean that one cos wave occurs in a pi interval? thanks in advance
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 9, 2010 #2

    ehild

    User Avatar
    Homework Helper

    Yes. pi is the angular frequency, w. How is it related to the time period, T?

    ehild
     
  4. Sep 9, 2010 #3

    Mark44

    Staff: Mentor

    I don't think so. You could write this function as x(t) = 10 cos(pi(t - 1/4)). The graph of x(t) = 10 cos(pi*t) has two transformations: a vertical expansion by a factor of 10 (that's your amplitude), and a compression toward the vertical axis by a factor of pi. This compression means that instead of having t intercepts at +/-pi/2, +/-3pi/2, +/-5pi/2, and so on, x(t) = 10 cos(pi*t) has t intercepts at +/-1/2, +/-3/2, +/-5/2, and so on.
    The -1/4 term causes a shift to the right by 1/4 unit of the graph of x(t) = 10 cos(pi*t).
     
  5. Sep 9, 2010 #4
    thanks for the help! T is 2pi/w so the period i got was 2. one cos wave occurs within 0-2
     
  6. Sep 9, 2010 #5

    ehild

    User Avatar
    Homework Helper

    Yes, but do not forget that it is shifted, so its has the maximum value where (pi*t)-(pi/4)=0.

    ehild
     
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