6) Let $v_1 = \begin{pmatrix} 1 \\ 0 \\ 0 \end{pmatrix}$, $v_2 = \begin{pmatrix} -1 \\ 1 \\ 1 \end{pmatrix}$, $v_3 = \begin{pmatrix} 1 \\ 1 \\ 0 \end{pmatrix}$, $v_4 = \begin{pmatrix} 1 \\ 0 \\ 1 \end{pmatrix}$.
a) Are $v_1, v_2, v_3, v_4$ linearly independent? Explain.
b) Are $v_1, v_2, v_3$ linearly independent? Explain.
