Question

How do you find the slope that is perpendicular to the line `3x-9y=15`?

Answer 1

The slope of the line perpendicular to line `3x-9y=15` is `-3`

Explanation:

When using the equation of a line, one calculates the value of `y` in terms of `x`, say `y=mx+c`, then `m` is the slope of the line and `c` is its intercept on `y`-axis.

As `3x-9y=15` can be written as `3x-15=9y` or

`y=3/9x-15/9` or `y=1/3x-5/3`

Hence slope of `3x-9y=15` is `1/3`

Product of slopes of two perpendicular lines is `-1`

Hence, the slope of the line that is perpendicular to the line `3x-9y=15` is `-1/(1/3)=-1xx3/1=-3`

graph{(3x-9y-15)(3x+y+5)=0 [-10, 10, -7.04, 2.96]}