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Math Help - areas of two spheres

  1. #1
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    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.
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  2. #2
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    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.
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