\(we\ have\ \frac{dN}{dx}=P\sin\theta\cdot\frac{d\theta}{dx}\)
\(x=R\cdot\left(1-\cos\theta\right)\)
\(\frac{dx}{d\theta}=R\cdot\sin\theta\)
\(Therefore\ \frac{dN}{dx}=\frac{P}{R}\)
=> \(\frac{d^2N}{dx^2}=0\)
similarly
\(\frac{d^2M}{dx^2}=0\)
As these 2 terms became zero which eliminates the term \(e_0a\)
Therefore neutral axis doesn't vary with \(e_0a\)