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m0nk3y

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**[SOLVED] GRIFFITH 3.18 Please explain how they got this**

## Homework Statement

The potential at the surface of a sphere (radius R) is given by Vo=kcos3[tex]\theta[/tex]\where k is a constant. find the potential inside and outside the sphere.

## Homework Equations

Their first step was:

Vo([tex]\theta[/tex]) = k[4cos^3[tex]\theta[/tex] - 3cos[tex]\theta[/tex] ]

how did they get this?