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Math Help - simplify expression of sine

  1. #1
    Newbie
    Joined
    Nov 2010
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    23

    simplify expression of sine

    How do you answer this one.


    What is the complex expression for a given alternating current,
    i = 250sin(\omega t - 25 ^ \circ)

    a. 227 + j106
    b. 160 - j75
    c. 227 - j106
    d. 160 + j75
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  2. #2
    Senior Member
    Joined
    Dec 2010
    Posts
    470
    For the current
    A\sin(\omega t + \phi)
    The amplitude is A and phase angle is \phi.
    For this problem A = 250 and \phi = -25^o.

    I think the complex expression being asked is the one with the given amplitude and phase angle.
    This is a + jb with
    a^2 + b^2 = A^2 and
    b/a = tan(\phi)

    So the answer is closest to (c): 227 - j106
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