18. A function f(x, y, z) is called harmonic in a region D in space if it satisfies the Laplace equation: Vf = v. Vf = as + 32s əx2 əy2 = 0 throughout D. a) Suppose that f is a harmonic function throughout a bounded region enclosed by a smooth surface S and that n is the chosen unit normal vector on S. Show that the integral over S of Vf n, the derivative of f in the direction of n is zero. b) Show that if f is harmonic on D, then ff, fVf n do = SSS, IVfl? dV.

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Chapter2: Second-order Linear Odes
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18.

18. A function f(x, y, z) is called harmonic in a region D in space if it satisfies the Laplace equation:
a² f
a² f
v²f = V.Vf:
=
a²f
+ + = 0 throughout D.
əx² дуг ?z2
a)
Suppose that f is a harmonic function throughout a bounded region enclosed by a smooth surface S and
that n is the chosen unit normal vector on S. Show that the integral over S of Vf. n, the derivative of f in
the direction of n is zero.
b) Show that if f is harmonic on D, then ff ƒVƒ ·ndo = SSS, Vƒ|² dv.
Transcribed Image Text:18. A function f(x, y, z) is called harmonic in a region D in space if it satisfies the Laplace equation: a² f a² f v²f = V.Vf: = a²f + + = 0 throughout D. əx² дуг ?z2 a) Suppose that f is a harmonic function throughout a bounded region enclosed by a smooth surface S and that n is the chosen unit normal vector on S. Show that the integral over S of Vf. n, the derivative of f in the direction of n is zero. b) Show that if f is harmonic on D, then ff ƒVƒ ·ndo = SSS, Vƒ|² dv.
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