Answer
$-2x-y=0$
Work Step by Step
The result of exercise 31 tells us that ${\bf v}=\langle a,\ \ b \rangle$ is perpendicular to lines $ax+by=c$.
Here, ${\bf v}=\langle -2,\ -1 \rangle$ and the lines are $-2x-y=c.$
Since $P(-1,2)$ is on the line, its coordinates satisfy the line equation
$\left\{\begin{array}{l}
-2(-1)-(2)=c\\
c=0
\end{array}\right.$
So the line equation is: $\quad -2x-y=0$
To graph the line, use the given point and $(0,0)$.
