3. Use method of undetermined coefficients 2X y" - 4y = 8xe

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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Question

Can you solve this equation using the given flow for the method of undetermined coefficients?

3. Use method of undetermined coefficients

y'' - 4y = 8xe2x

Example 2
Find the general solution : y" + 2y' + y = 7 + 75 sin 2x
Solution:
Thus,
m² + 2m + 1 = 0
Yp =
=
=
(m+1) (m+1) = 0
Yc = C₁ ex + C₂ xe-x
R(x) = 7+75 sin 2x
A + B cos 2x + C sin 2x
Yp
-2B sin 2x + 2C cos 2x
Yp" = -4B cos2x · 4C sin 2x
suggests roots of 0 and +2i
- 4B cos 2x -4Csin 2x + 2(-2B sin 2x + 2C cos 2x) + A + B cos 2x + C sin 2x = 7+75 sin 2x
Equating coefficients :
Solving simultaneously
for constant : A = 7
Cos 2x - 4B + 4C + B = 0
Sin 2x : -4C-4B + C = 75
4C3B = 0
-3C-4B = 75
B = -12 and C= -9 yp = 7-12 cos 2x - 9 sin 2x
The general solution is
y=ex (C₁ + C₂ x) + 7-12 cos 2x - 9 sin 2x
Transcribed Image Text:Example 2 Find the general solution : y" + 2y' + y = 7 + 75 sin 2x Solution: Thus, m² + 2m + 1 = 0 Yp = = = (m+1) (m+1) = 0 Yc = C₁ ex + C₂ xe-x R(x) = 7+75 sin 2x A + B cos 2x + C sin 2x Yp -2B sin 2x + 2C cos 2x Yp" = -4B cos2x · 4C sin 2x suggests roots of 0 and +2i - 4B cos 2x -4Csin 2x + 2(-2B sin 2x + 2C cos 2x) + A + B cos 2x + C sin 2x = 7+75 sin 2x Equating coefficients : Solving simultaneously for constant : A = 7 Cos 2x - 4B + 4C + B = 0 Sin 2x : -4C-4B + C = 75 4C3B = 0 -3C-4B = 75 B = -12 and C= -9 yp = 7-12 cos 2x - 9 sin 2x The general solution is y=ex (C₁ + C₂ x) + 7-12 cos 2x - 9 sin 2x
3. Use method of undetermined coefficients
2X
y" - 4y =
8xe
Transcribed Image Text:3. Use method of undetermined coefficients 2X y" - 4y = 8xe
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