Give algebraic and geometric descriptions of $\operatorname{Span} \{ a_1, a_2, a_3, a_4 \}$ where
$a_1 = (1, -1, -2), a_2 = (3, -3, -1), a_3 = (2, -2, -4), a_4 = (2, -2, 1)$
So far, I have: $ \begin{matrix} \;\;\,1 & \;\;\,3 & \;\;\,2 & \;\;\,2 \\ -1 &-3 &-2 &-2\\ -2 & -1 &-4 & \;\;\,1 \\ \end{matrix} $ Though, I feel like I'm missing a column. What should this system be equal to?