4. (10%) Let $$x1 = \begin{bmatrix} 1 \\ -1 \\ 2 \\ 3 \end{bmatrix}$$, $$x2 = \begin{bmatrix} -2 \\ 3 \\ 1 \\ -2 \end{bmatrix}$$, and $$x_3 = \begin{bmatrix} 1 \\ 0 \\ 7 \\ 7 \end{bmatrix}$$. Determine whether the vectors are linearly independent.