Let D be a region to which Greens theorem applies and n the outward unit normal vector
Chapter 6, Problem 31(choose chapter or problem)
Let D be a region to which Greens theorem applies and n the outward unit normal vector to D. Suppose f (x, y) is a function of class C2. Show that D 2 f dA = D f n ds, where 2 f denotes the Laplacian of f (namely, 2 f = 2 f/x 2 + 2 f/y2) and f/n denotes f n. (See the proof of Theorem 2.3 for more information about n.)
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