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What is the equation for finding the d radius of a sphere 

 May 11, 2017
 #1
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+2

What information are you given?

Do you know the volume, the surface area, the circumference, or maybe the diameter?

 May 11, 2017
 #2
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I mean the radius and volume 

 

Surface area is 13r

 May 11, 2017
edited by Guest  May 12, 2017
 #3
avatar+7352 
+3

Oh okay...Assuming that the " r " in " 13r " stands for the radius......

 

The formula for the surface area of a sphere is:

surface area = 4π r2          Replace " surface area " with " 13r ".

13r = 4π r2                         Divide both sides of the equation by r.

13 = 4π r                            Divide both sides of the equation by 4π.

13/(4π) = r

So, the radius =  \(\frac{13}{4\pi}\)   units

 

The formula for the volume of a sphere is:

volume = \( \frac43 \pi r^3 \)                 Replace " r " with " \(\frac{13}{4\pi}\) ".

volume = \( \frac43 \pi (\frac{13}{4\pi})^3 \)           Simplify.

 

volume = \(\frac43\pi(\frac{2197}{64\pi^3}) = \frac43(\frac{2197}{64\pi^2}) = \frac{2197}{48\pi^2} \)     cubic units

 May 12, 2017

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