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Homework Help: Help needed on unkowns in a matrix

  1. Mar 21, 2010 #1
    1. The problem statement, all variables and given/known data
    the following 3 equations are given, show that alpha(a) has two non trival solutions, then solve for the whole thing:

    2. Relevant equations
    ax - 3y + ( 1+a) z = 0
    2x + y - az = 0
    (a+2)x - 2y + az = 0

    i think i may be missing something but i cant seem to even get started on this problem,
  2. jcsd
  3. Mar 21, 2010 #2


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    Science Advisor

    Well, what HAVE you done? You mention "unknowns in a matrix" so presumably you know how to set this up as a matrix equation. With A as the matrix of coefficients, X as the column matrix <x, y, z> and 0 as the column matrix <0, 0, 0>, your equation is AX= 0. The unique solution will be [itex]X= A^{-1}0= 0[/itex] as long as A has an inverse.

    So the question is, "for what values of a does this matrix of coefficients not have an inverse?" I don't know what methods of finding an inverse matrix you have learned but you might try row-reducing the matrix and see what values of a prevent you doing that. Or determine what values of a make the determinant of the matrix 0.
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