For a fi­rst-order DE dy/dx = f (x, y) a curve in the plane defi­ned by f (x, y) = 0 is called a nullcline of the equation, since a lineal element at a point on the curve has zero slope. Use computer software to obtain a direction ­field over a rectangular grid of points for dy/dx = x² - 2y, and then superimpose the graph of the nullcline y = 1/2 x² over the direction fi­eld. Discuss the behavior of solution curves in regions of the plane defi­ned by y < ½ x² and by y > ½ x². Sketch some approximate solution curves. Try to generalize your observations.