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Q9 E

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Fundamentals Of Differential Equations And Boundary Value Problems
Found in: Page 449
Fundamentals Of Differential Equations And Boundary Value Problems

Fundamentals Of Differential Equations And Boundary Value Problems

Book edition 9th
Author(s) R. Kent Nagle, Edward B. Saff, Arthur David Snider
Pages 616 pages
ISBN 9780321977069

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Short Answer

Find at least the first four non-zero terms in a power series expansion about x0 for a general solution to the given differential equation with the value for x0.

(x2-2x)y''+2y=0; x0=1

The first four nonzero terms in a power series expansion about x0 for a general solution:

y=a01+(x+1)2+13(x-1)4+...+a1x-1+13(x-1)3+...

See the step by step solution

Step by Step Solution

Step 1: Power series expansion

A power series expansion of can be obtained simply by expanding the exponential and integrating term-by-term. This series converges for all, but the convergence becomes extremely slow if significantly exceeds unity.

Step 2: To determine the first four nonzero terms in a power series expansion about x0 for a general solution.

x2-2xy''+2y=0y''+2x2-2xy=0

We get the value of q(x)=2x2-2x.

y(x)=n=0anx-1ny''(x)=n=2n(n-1)anx-1n-2+2n=0anx-1n=0

Let, x-1=t:

role="math" localid="1664089919710" (t+1)(t-1)n=2n(n-1)an(t)n-2+2n=0antn=0n=2n(n-1)an(t)n-n=2n(n-1)an(t)n-2+2n=0antn=02a2t2+6a3t3+12a4t4+20a5t5+...2a0+2a1t+2a2t2+2a3t3+2a4t4+...=0(2a0-2a2)+(2a1-6a3)(x-1)+(2a2-12a4+2a2)(x-1)2+(2a3-20a5)(x-1)3+....=02a0-2a2=0a2=a02a1-6a3=0a3=13a12a2-12a4+2a2=0a4=13a0

In the end,

y=n=0anx-1n=a0+a1(x-1)+a2(x-1)2+a3(x-1)3+...y=a01+(x+1)2+13(x-1)4+...+a1x-1+13(x-1)3+...

Hence, the final answer is y=a01+(x+1)2+13(x-1)4+...+a1x-1+13(x-1)3+...

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