Find all solutions to the homogeneous system $A \mathbf{x}=\mathbf{0}$ for the coefficient matrix
(a) $\left(\begin{array}{rr}3 & -1 \\ -9 & 3\end{array}\right)$,
(b) $\left(\begin{array}{rrr}2 & -1 & 4 \\ 3 & 1 & 2\end{array}\right)$,
(c) $\left(\begin{array}{rrrr}1 & -2 & 3 & -3 \\ 2 & 1 & 4 & 0\end{array}\right)$,
(d) $\left(\begin{array}{lll}1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9\end{array}\right)$,
(e) $\left(\begin{array}{rrr}0 & 2 & -1 \\ -2 & 0 & 3 \\ 1 & 3 & 0\end{array}\right)$,
(f) $\left(\begin{array}{rr}1 & -2 \\ 1 & -1 \\ 2 & -1 \\ 1 & 0\end{array}\right)$,
(g) $\left(\begin{array}{rrr}1 & 2 & 0 \\ -1 & -3 & 2 \\ 4 & 7 & 2 \\ -1 & 1 & 6\end{array}\right)$,
(h) $\left(\begin{array}{rrrr}0 & 0 & 3 & -3 \\ 1 & -1 & 0 & 3 \\ 2 & -2 & 1 & 5 \\ -1 & 1 & 1 & -4\end{array}\right)$.