Question 896090
Keeping the slope of the given line as m, let {{{M=-(1/m)}}}, and M is the slope for any line perpendicular to y=mx+b.


Also notice {{{b=y-mx}}}.


The wanted line parallel:
{{{highlight(y=mx+(c-m*a))}}}.


The wanted line perpendicular:
{{{highlight_green(y=Mx+(c-Ma))}}}
but in case you want this in terms of m of the given equation,
{{{y=-(1/m)x+(c-(-(1/m))a)}}}
{{{highlight(y=-x/m+(c+a/m))}}}