Answer Exercise 3.3 .1 for (a) $\left(\begin{array}{r}2 \\ -1\end{array}\right),\left(\begin{array}{r}1 \\ -2\end{array}\right)$,
(b) $\left(\begin{array}{r}1 \\ 0 \\ -1\end{array}\right),\left(\begin{array}{r}-1 \\ 1 \\ 0\end{array}\right)$,
, (c) $\left(\begin{array}{r}1 \\ -2 \\ -1\end{array}\right),\left(\begin{array}{r}2 \\ -1 \\ -3\end{array}\right)$.