Recall from Section 14.3 that a function g is called harmonic on D if it satisfies Laplace’s equation, that is, ∇²g = 0 on D. Use Green’s first identity (with the same hypotheses as in Exercise 33) to show that if g is harmonic on D, then ∮_CD_ngds = 0. Here D_ng is the normal derivative of t defined in Exercise 33.