Question 135170
All you know in this case is the slope of a parallel or perpendicular 
line. If the equation is {{{y = 3x + 9}}}, then a parallel line
will have slope = {{{3}}}.
A perpendicular line will have slope = {{{-(1/3)}}}. You can write general
equations in which the y-intercept is unknown like this:
{{{y = 3x + b}}} for a parallel line
{{{y = -(1/3)x + b}}} for a perpendicular line
In the parallel case, {{{b}}} shouldn't be {{{9}}}, since that would
make it the same line as the original.