GRIFFITH 3.18 Please explain how they got this

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The discussion focuses on deriving the potential at the surface of a sphere given by Vo = kcos3θ. Participants explain that the expression Vo(θ) = k[4cos^3θ - 3cosθ] is obtained using a trigonometric identity, specifically the triple angle formula for cosine. This identity helps transform cos3θ into a polynomial form involving cosθ. The conversation emphasizes the importance of understanding trigonometric identities in solving potential problems in physics. Ultimately, the derivation clarifies how to express the potential both inside and outside the sphere.
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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\theta\where k is a constant. find the potential inside and outside the sphere.


Homework Equations


Their first step was:
Vo(\theta) = k[4cos^3\theta - 3cos\theta ]


how did they get this?

The Attempt at a Solution

 
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