# Thread: areas of two spheres

1. ## areas of two spheres

This came from an engineering board exam and I can't solve it.

Find approximately the difference between the areas of two spheres whose radii area 4 ft. and 4.05 ft.

2. The surface area of a sphere is $S=4\pi r^2$. I'm guessing that the problem wants you to use differentials to get the approximation.

$dS = 8\pi rdr = 8\pi (4)(.05) = 1.6\pi$.