Explanation Given: The given initial value problem is, ∂ 2 u ∂ t 2 = 9 ∂ 2 u ∂ x 2 , 0 < x < π , t > 0 u ( 0 , t ) = u ( π , t ) = 0 , t > 0 u ( x , 0 ) = sin 4 x + 7 sin 5 x , 0 < x < π ∂ u ∂ t ( x , 0 ) = { x , 0 < x < π 2 π − x , π 2 < x < π Approach: The motion of the string initial boundary value problem is given by, ∂ 2 u ∂ t 2 = α 2 ∂ 2 u ∂ x 2 , 0 < x < L , t > 0 u ( 0 , t ) = u ( L , t ) = 0 , t > 0 u ( x , 0 ) = f ( x ) , 0 < x < L ∂ u ∂ t ( x , 0 ) = g ( x ) , 0 < x < L The formal solution is determined by method of separation of variables. u ( x , t ) = ∑ n = 1 ∞ [ a n cos n π α L t + b n sin n π α L t ] sin n π x L … ( 1 ) Here, a n = 2 L ∫ 0 L f ( x ) sin n π L x d x ( 2 ) b n = ( L n π ) 2 L ∫ 0 L g ( x ) sin n π L x d x ( 3 ) f ( x ) = ∑ n = 1 ∞ a n sin n π x L ( 4 ) g ( x ) = ∑ n = 1 ∞ b n ( n π α L ) sin n π x L ( 5 ) Calculation: Consider the given initial value problem. ∂ 2 u ∂ t 2 = 9 ∂ 2 u ∂ x 2 , 0 < x < π , t > 0 u ( 0 , t ) = u ( π , t ) = 0 , t > 0 u ( x , 0 ) = sin 4 x + 7 sin 5 x , 0 < x < π ∂ u ∂ t ( x , 0 ) = { x , 0 < x < π 2 π − x , π 2 < x < π Compare the above initial value problem with motion of the string initial boundary value problem. α = 3 L = π f ( x ) = sin 4 x + 7 sin 5 x g ( x ) = { x , 0 < x < π 2 π − x , π 2 < x < π Substitute π for L in equation ( 4 ) . f ( x ) = ∑ n = 1 ∞ a n sin n π x L = ∑ n = 1 ∞ a n sin n x = a 1 sin x + a 2 sin 2 x + a 3 sin 3 x + a 4 sin 4 x + a 5 sin 5 x = sin x + 7 sin 5 x Compare the coefficient of like terms a 4 = 1 a 5 = 7 a n = 0 for all n ≠ 4 , n ≠ 5 Substitute 3 for α and π for L in equation ( 5 ) . g ( x ) = ∑ n = 1 ∞ b n ( 3 n π π ) sin n π x π = ∑ n = 1 ∞ b n ( 3 n ) sin n x Substitute 3 for α and π for L in equation ( 1 )

Fundamentals of Differential Equations [With CDROM] - 7th Edition

7th Edition

ISBN: 9780321410481

Author: Saff, Edward B., Snider, Arthur David, Nagle, R. Kent

Publisher: Addison Wesley

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Chapter 10.6, Problem 4E

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The formal solution of initial boundary problem.

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Fundamentals of Differential Equations [With CDROM] - 7th Edition

Ch. 10.2 - In Problems 1-8, determine all the solutions, if...Ch. 10.2 - Prob. 2E Ch. 10.2 - Prob. 3E Ch. 10.2 - Prob. 4E Ch. 10.2 - In Problems 1-8, determine all the solutions, if...Ch. 10.2 - Prob. 6E Ch. 10.2 - In Problems 1-8, determine all the solutions, if...Ch. 10.2 - In Problems 1-8, determine all the solutions, if...Ch. 10.2 - In Problems 9-14, find the values of eigenvalues...Ch. 10.2 - In Problems 9-14, find the values of eigenvalues...

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Solution Summary: The author explains the motion of the string initial boundary value problem.

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To find:

The formal solution of initial boundary problem.