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Homework Help: Kirchoff's Rules, Mathmatical/Logic help?

  1. Apr 13, 2010 #1
    Hello all. I feel like such a retard, but there's an example problem in my book with the answer, and I just don't know how they are getting the answer. I suppose it's due to my lack of mathematical skills. I was wondering if someone could guide me on how they got the answer.

    [PLAIN]http://img406.imageshack.us/img406/5328/kirchoff.jpg [Broken]

    The answer is at the bottom. I just don't understand how they are getting IofA, IofB, and IofH. I do realize that I = V/R, but I'm confused because their are 2 unknown variables in each question. I apologize in advance for my stupidity. :(
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 13, 2010 #2
    For one thing, there must be one more equation as there are three unknowns. I suppose the third one comes form the first Kirchoff's rule applied to one of the nodes.

    So you'll have 3 equations and 3 unknowns. There are several methods to solve linear systems of equations.
    You don;t know any of them?
    The most straightforward (not always the simpler) is to solve one equation for one of the unknowns (in terms of the other unknowns) and replace the expression in the other two. You'll have two equations with two unknowns. Then you repeat the procedure.
  4. Apr 13, 2010 #3


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    Please attach the circuit diagram.
  5. Apr 13, 2010 #4
    Ah, I apologize, didn't know the first equation that they gave was really relevant in solving the problem. But yeah, I took about a 6 year break from college, and it's been about 8 years since I've taken a dedicated math course, so I've mostly just forgot how to do this kind of math. Most of the things are coming back to me after I see how they are done though.

    Sorry about that. Hope this helps:

    [PLAIN]http://img697.imageshack.us/img697/4229/kirchoff2.jpg [Broken]
    Last edited by a moderator: May 4, 2017
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