Chapter 1 - Linear Equations in Linear Algebra - Supplementary Exercises - Page 90: 8

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2 out of three columns must be pivot columns. First and second: \[ \left[\begin{array}{lll} \square & * & * \\ 0 & & * \end{array}\right] \] First and third: \[ \left[\begin{array}{lll} \square & * & * \\ 0 & 0 & \end{array}\right] \] Second and third: \[ \left[\begin{array}{lll} 0 & & \\ 0 & 0 & \end{array} *\right] \] b) All three columns must be pivot. \[ \left[\begin{array}{lll} \square & * & * \\ 0 & & * \\ 0 & 0 & \end{array}\right] \]