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How do i solve the system of equation

  1. Jun 22, 2010 #1
    1. The problem statement, all variables and given/known data
    I need to find a,b,c from
    a+b-c=0.1
    2a-b-c=0
    a+b+c=0.3


    2. Relevant equations



    3. The attempt at a solution

    The furthest Ive gone is
    a+b+c=0.1
    3a=0.3=>0.1

    NOW PLEASE HELP ME HOW TO SOLVE FOR B AND C ????
     
  2. jcsd
  3. Jun 22, 2010 #2
    im not sure what you have done?
    you can start by subtracting the first equation from third equation, then you will have the value of c
    after that you can use this value in the second equation to get either a in terms of b or b in terms of a, after that you can easily substitute again in the first or third equation to get your answer..
     
  4. Jun 22, 2010 #3

    Mark44

    Staff: Mentor

    You lost your variable! 3a = .3 ==> a = .1
    Now substitute for a in two other equations to get two equations in b and c, which you can solve for those variables.
     
  5. Jun 22, 2010 #4

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    What you did the first time was add the second and third equations, eliminating both b and c at the same time to get a= .1.

    Now, you can, as Mark44 suggests, set a= .1 in those three equations reducing to two equations for b and c. (Only two equations because a= .1 makes the second and third equations, that you used to get a, the same.)

    Or you can do as Thebigstar25 suggests- subtract the first equation from the third equation. That eliminates both a and b at the same time, allowing you to solve for c.

    Once you have found a and c, put those values into any of the three equations and solve for b.
     
  6. Jun 22, 2010 #5
    Ok thanks for the fast reply because it really helped !
     
  7. Jun 22, 2010 #6
    I do not know if you have learned about Cramer's Rule, but you might want to look into this, it will make this problem very simple to solve.
     
    Last edited: Jun 22, 2010
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