Solution
= Solution
The $\phi$ part contributes $-\sin\phi/(r^2\sin^2\theta)$, and again $1/r$ is radially harmonic. Hence
$$
\boxed{u=\frac{\sin\phi}{r}.}
$$
= Solution
The $\phi$ part contributes $-\sin\phi/(r^2\sin^2\theta)$, and again $1/r$ is radially harmonic. Hence
$$
\boxed{u=\frac{\sin\phi}{r}.}
$$