so if a slope of two lines is 4/a and -7, determine the value of a if the lines are parallel, and if they are perpendicular.
Parallel means the slope is the same so 4/a = -7 solve for 'a'
Perpindicular means one slope is -1/other
so 4/a = - 1/-7
4/a = 1/7 solve for 'a'