Question 133953
If you are given the equations of the lines, solve the equations for y in terms of x -- in other words put them into slope-intercept form, {{{y=mx+b}}}.  Then compare the slopes of the two lines.  Two lines are perpendicular if and only if their slopes are negative reciprocals of each other.  That is to say if {{{m[1]}}} is the slope of one of the lines and {{{m[2]}}} is the slope of the other line, the lines are perpendicular if and only if {{{m[1]=-(1/m[2])}}}.