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Homework Help: Complex numbers, Homework Question.

  1. Oct 1, 2007 #1
    Express this in terms of j


    I have no idea how to do the ones with square roots, my teacher is lost. Completely and im stuck on this 1 number for like 2 hrs trying to figure it out.

    The answer is sopose to be -28j please help me out

    **Note that j2= -1

    NOTE ALSO THAT the 2 is a 5jsquare
  2. jcsd
  3. Oct 1, 2007 #2


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    You seem to have written the given expression incorrectly. The question itself seems incredibly simple. Can we assume that for "j", you mean j*j= -1 ? Let me try to continue:

    [note, you might really want to see the part below starting with "Where..." ]
    6j - 5j2(-63)^(0.5)
    6j -5*2*j*j(3*3*7)^(0.5)
    6j -5*2*3*(-1)*(7^0.5)
    6j + 30*7^(0.5)

    Where did you find j2 = -1 ? Is that simply a given condition? "2" is a subscript?
    6j - 5j2(-63)^(0.5)
    6j + 5*(-1)*3*(7^(0.5))
    6j - 15*(7^(0.5))
  4. Oct 1, 2007 #3


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    Oh, those engineers and their jmaginary numbers!

    Any normal person would use "i" but those engineers have to use "j"!
    I assume you mean 6j-5j^2√-63. If you won't use LaTex at least use ^2 to indicate squares. Yes, J^2= -1 so obviously [itex]6j- 5j^2\sqrt{-3}= 5j\sqrt{63}+ 6j= (5\sqrt{63}+6)j[/itex]. What more is there to say?
  5. Dec 1, 2008 #4
    It should be [tex]\sqrt{-63}[/tex] in your first equation. You confused the heck out of me for a few minutes :wink:
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