We have the points P(ap^2,\,2ap) and Q(aq^2,\,2aq)
a) The equation of a line joining two points may be found by calculating the gradient (i.e. rise/run) using the two points, and then using the point-gradient formula (y-y_1) = m(x-x_1) with either point.
b) If two lines are perpendicular...