1) When we find the area of a region bounded by an upper curve f(x) and a Lower curve g(x), we integrate f(x)-g(x). Analytically, how do we know that this integral is positive and so actually represents the area.

2) Rotate a circle of radius r around the x-axis and use the method of disks to prove the formula for the volume of a sphere of radius r.

3) Describe what methods would force you to use the method of washers rather than the method of disks.