Answer
$-x-y=1$
Work Step by Step
The result of exercise 32 tells us that ${\bf v}=a{\bf i} + b{\bf j}$
is parallel to the lines $bx-ay=c$
Here, ${\bf v}=1\cdot{\bf i} + (-1)\cdot{\bf j}$,
$a=1,\quad b=-1,$
and the lines are $-x-y=c.$
$P(-2,1)$ is on the line $\Rightarrow \left\{\begin{array}{l}
-(-2)-(1)=c\\
c=1
\end{array}\right.$
so the line equation is $\quad -x-y=1$
(a second point on the line is $(-1,0)$ )
