# areas of two spheres

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• Dec 7th 2010, 03:46 AM
SamanthaMathGirl
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.
• Dec 7th 2010, 03:54 AM
DrSteve
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.

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