(Solved): Exercises \( 19 \square \) and \( 20 \square \) use the notation of Example \( 1 \square \) for ma ...

Exercises \( 19 \square \) and \( 20 \square \) use the notation of Example \( 1 \square \) for matrices in echelon form. Suppose each matrix represents the augmented matrix for a system of linear equations. In each case, determine if the system is consistent. If the system is consistent, determine if the solution is unique. 20. a. \[ \left[\begin{array}{lll} \mathbf{-} & * & * \\ 0 & \boldsymbol{*} & * \\ 0 & 0 & 0 \end{array}\right] \] b. \[ \left[\begin{array}{lllll} \boldsymbol{\Xi} & * & * & * & * \\ 0 & 0 & \boldsymbol{\Xi} & * & * \\ 0 & 0 & 0 & \boldsymbol{} & * \end{array}\right] \]