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Homework Help: Simultaneous equations

  1. Mar 16, 2008 #1
    1. The problem statement, all variables and given/known data

    It's been a while since I solved these kind of things. I can only remember how to solve 2 simultaneous equations

    40x + 40y = 10
    -40y -40z = -2
    40x - 40z = 8

    2. Relevant equations


    3. The attempt at a solution
    Just need a pointer on what method to use.
  2. jcsd
  3. Mar 16, 2008 #2


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    You can put them in a matrix or row-reduce. But since the coefficients are very much alike, you can also try to do it more efficiently.
    For example, you can use the latter two to eliminate z and then solve the remaining system of two. Then plug the solutions back into either of the last ones, and find z.
  4. Mar 16, 2008 #3
    1) Divide all by 40. (This should simplify alot)
    2) Solve for y in terms of x (first equation)
    3) Plug in for y (from equation 1) in the second equation, and solve for x. (Your y is in terms of x, so this should be easy)
    4) Now, plug in the x that you found in the second equation (in terms of z), into the last equation. You'll find z. From there it's easy.

    And of course, this is just one of the many ways to do it in this method.
  5. Mar 17, 2008 #4
    Use cross multiplication method.
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