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Math Help - [SOLVED] System of Linear Equations

  1. #1
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    [SOLVED] System of Linear Equations

    I have another question regarding another problem. The system is:

    x + y = 0
    y + z = 0
    x + z = 0
    ax + by + cz = 0

    Find values for a, b, and c so that the system has:
    (a) a unique solution
    (b) no solution
    (c) an infinite number of solutions

    I know for a fact it is not possible for this system to have no solution. It has the trivial solution x = y = z = 0. Also, it seems if a + b + c != 0, then it may have an infinite number of solutions. To be honest aside from already knowing part b, I am not quite certain how to proceed. Thanks again for help!
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  2. #2
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    Quote Originally Posted by Alterah View Post
    I have another question regarding another problem. The system is:

    x + y = 0
    y + z = 0
    x + z = 0
    ax + by + cz = 0

    Find values for a, b, and c so that the system has:
    (a) a unique solution
    (b) no solution
    (c) an infinite number of solutions

    I know for a fact it is not possible for this system to have no solution. It has the trivial solution x = y = z = 0. Also, it seems if a + b + c != 0, then it may have an infinite number of solutions. To be honest aside from already knowing part b, I am not quite certain how to proceed. Thanks again for help!

    Subtract the second from the first:
    x + y = 0 Equation1
    y + z = 0 Equation2
    ---------------
    x - z = 0 Difference

    x + z = 0 Equation3

    If x-z =0 AND x+z = 0
    THEN there is a finit number of solutions.

    ax + by + cz = 0
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  3. #3
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    That makes sense. I apologize if I am a little slow on recognizing a few things. I am very tired at the moment. That makes sense regarding the two equations:

    x - z = 0 and x + z = 0. But, to be honest I am not seeing how to link that with a, b, and c.
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  4. #4
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    Of course, x+ z= 0 and x- z= 0 can only be true if x= z= 0. Then x+ y= 0 immediately gives y= 0. That has nothing at all to do with "ax+ by+ cz= 0", except that it is also satisifed by x= y= z= 0. The system has only the single solution x= y= z= 0 no matter what a, b, c are.
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  5. #5
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    Yeah, I realized that shortly before I needed to hand the assignment in. Thanks for the help!
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