4. Suppose that in the plate described in Example 2, Sec. 43, there is a heat source de- pending on the variable y and that the entire boundary is kept at temperature zero. According to Sec. 23, the steady temperatures u(x, y) in the plate must now satisfy Poisson's equation Uxx (x, y) + Uyy(x, y) +q(y) = 0 (a) By assuming a (bounded) solution of the form u(x, y) = u(x, y) n=1 of this temperature problem and using the method of variation of parameters (Sec. 42), show formally that = 8 B₁(x) = B₂ (x) sin ny (n = 1, 2,...), where qn are the coefficients in the Fourier sine series for q(y) on the interval 0 0,0

Advanced Engineering Mathematics
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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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4
4. Suppose that in the plate described in Example 2, Sec. 43, there is a heat source de-
pending on the variable y and that the entire boundary is kept at temperature zero.
According to Sec. 23, the steady temperatures u(x, y) in the plate must now satisfy
Poisson's equation
Uxx (x, y) + Uyy(x, y) +q(y) = 0
(a) By assuming a (bounded) solution of the form
u(x, y) =
u(x, y)
n=1
of this temperature problem and using the method of variation of parameters
(Sec. 42), show formally that
=
8
B₁(x) =
B₂ (x) sin ny
(n = 1, 2, ...),
where qn are the coefficients in the Fourier sine series for q(y) on the interval
0 <y<л.
4Q
408
qn
12 (1- e-mx)
(b) Show that when q(y) is the constant function q(y) = Q, the solution in part (a)
becomes
(x>0,0<у<л).
1- exp[-(2n-1)x]
(2n-1)³
sin (2n-1)y.
n=1
Suggestion: In part (a), recall that the general solution of a linear second-order
equation y" + p(x)y g(x) is of the form y=ye+ Yp, where Ур is any particular
solution and ye is the general solution of the complementary equation
=
y" + p(x) y = 0.¹
Transcribed Image Text:4. Suppose that in the plate described in Example 2, Sec. 43, there is a heat source de- pending on the variable y and that the entire boundary is kept at temperature zero. According to Sec. 23, the steady temperatures u(x, y) in the plate must now satisfy Poisson's equation Uxx (x, y) + Uyy(x, y) +q(y) = 0 (a) By assuming a (bounded) solution of the form u(x, y) = u(x, y) n=1 of this temperature problem and using the method of variation of parameters (Sec. 42), show formally that = 8 B₁(x) = B₂ (x) sin ny (n = 1, 2, ...), where qn are the coefficients in the Fourier sine series for q(y) on the interval 0 <y<л. 4Q 408 qn 12 (1- e-mx) (b) Show that when q(y) is the constant function q(y) = Q, the solution in part (a) becomes (x>0,0<у<л). 1- exp[-(2n-1)x] (2n-1)³ sin (2n-1)y. n=1 Suggestion: In part (a), recall that the general solution of a linear second-order equation y" + p(x)y g(x) is of the form y=ye+ Yp, where Ур is any particular solution and ye is the general solution of the complementary equation = y" + p(x) y = 0.¹
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