86. The folium of Descartes is the curve with equation x3 + y3 = 3axy, where a * 0 is a constant (Figure 25). a. Show that the line y = tx intersects the folium at the origin and at one other point P for all t -1, 0. Express the coordinates of P in terms of t to obtain a parametrization of the folium. Indicate the direction of the parametrization on the graph. b. Describe the interval of t-values parametrization the curve in quadrants I, II, and IV. Note that t =-1 is a point of discontinuity of the parametrization. c. Calculate dy / da as a function of t and find the points with horizontal or vertical tangent