Acho que é para usar a fórmula
Let r be a positive constant. Consider the cylinder
and let C be the part of the cylinder that satisfies 
.c) Let a be the length of the arc along the base circle of C from the point (r,0,0) to the point (
Let b be the length of the line segment from the point ( to the point . Express a and b in terms of .
d) Calculate the area of the side of C with , and express it in terms of r.
por 
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