You have a line:
y=mx+b (slope-intercepted form)
m=slope of this line.
The slope of a line perpendicular to that given line will be: ´"m´"
m´=-1/m.
For example:
y=8x+3
m=8
The solpe fo a line perpendicular to "y=8x+3" is:
m`=-1/8
On't want to be ripped off do you?/ That's why you want to have some interest. Just in a simple form this is a rush job right now.