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Math Help - complex numbers question help

  1. #1
    Newbie
    Joined
    Nov 2010
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    3

    complex numbers question help

    can someone tell me where i have gone wrong i am stuck on this last question, i am pretty sure i have done something wrong:

    I have to do product over sum to combine the two equations

    Z1 X Z3
    -------
    Z1 + Z3

    Z1=10+J30 Z3=2-J20

    Z1= 31.6 <71.5 degrees
    Z3= 20 <84.2 degrees

    (31.6<71.5)(20<84.2) 632<155.7
    --------------------- = ------------
    (10+J30)+(2-J20) 12+j10

    -576 + J260
    = ------------
    12 + J10

    (-576+J260)(12-J10)
    = ---------------------
    (12+J10)(12-J10)

    -6912+J5760+3120-J2600
    = -------------------------
    144-120J+120J-J^2 100

    -3792 + J3160
    = ---------------
    144-100


    Have i gone wrong as this does not seem correct?
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  2. #2
    A Plied Mathematician
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    CT, USA
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    Yeah, you've made a mistake in there somewhere. I would advise against going to the polar representation to do the multiplication, as the trig functions have ambiguities. You can do the multiplication in rectangular coordinates. Just foil it out, and use j^{2}=-1. What do you get?
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