Question

How do you find the slope that is perpendicular to the line `x-3y=9`?

Answer 1

Any line perpendicular to `x-3y=9` has a slope of `-3`

Explanation:

A line in the form `Ax+By=C` has a slope of `m=-A/B`

If a line has a slope of `m` then every line perpendicular to it has a slope of `-1/m`

For the given example `1x-3y=9` has a slope of `-(1/(-3))=1/3`
and
any line perpendicular to it has a slope of
`color(white)("XXX")-1/((1/3))=-3`