# GRIFFITH 3.18 Please explain how they got this

1. Feb 18, 2008

### m0nk3y

[SOLVED] GRIFFITH 3.18 Please explain how they got this

1. The problem statement, all variables and given/known data
The potential at the surface of a sphere (radius R) is given by Vo=kcos3$$\theta$$\where k is a constant. find the potential inside and outside the sphere.

2. Relevant equations
Their first step was:
Vo($$\theta$$) = k[4cos^3$$\theta$$ - 3cos$$\theta$$ ]

how did they get this?

3. The attempt at a solution

2. Feb 18, 2008

trig ID!