given a linear equation in slope- intercept form y = mx + c
where m is the slope and c the y -intercept
the slope of a line perpendicular to it is - [tex]\frac{1}{m}[/tex]
If equation is y = 2x + 3 ( with slope m = 2 )
then the perpendicular slope = - [tex]\frac{1}{2}[/tex]
