The graphs of the two linear equations ax + by = c and bx - ay = c, where a, b and c are all not equal to zero, A. are parallel B. intersect at one point but not perpendicular C. intersect at two points D. perpendicular Solution let us find the slopes of the two lines a x + b y = c , slope m1 = - a / b b x - a y = c , slope m2 = b / a m1*m2 = (- a / b)(b / a) = - 1 The two lines are perpendicular.