VIDEO ANIMATION: solid of revolution 5 (line above and below X axis)

MATHEMATICS solids of revolution. This animation starts with a curve (y=fx) that goes above and below the X axis. The positive and negative ares bounded by the curve are then limited by two boundaries to create two areas (red). This region then rotates about the X axis to create a solid of revolution. Note that even though the curve becomes negative it still produces a solid figure.