D2-4D+4D=x2+ex+cos2x
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Answer:
(D2−4D+4)y=0
(D−2)2y=0
D=2
yh=C1e2x+C2xe2x
Solve non-homogeneous equation using Method of Variation of Parameters.
(D2−4D+4)y=x2e2xcos(2x)
y1=e2x
y2=xe2x
W(y1,y2)=y1y2′−y1′y2=(e2x)((2x+1)e2x)−(2e2x)(xe2x)=e4x
g(x)=x2e2xcos(2x)
u1=−∫y2g(x)W(y1,y2)dx=−∫xe2x⋅x2e2xcos(2x)e4xdx=−∫x3cos(2x)dx=(34x−12x3)sin(2x)+(38−34x2)cos(2x)
u2=∫y1g(x)W(y1,y2)dx=∫e2x⋅x2e2xcos(2x)e4xdx=∫x2cos(2x)dx=(12x2−14)sin(2x)+12xcos(2x)
yp=u1y1+u2y2=[(34x−12x3)sin(2x)+(38−34x2)cos(2x)]e2x+[(12x2−14)sin(2x)+12xcos(2x)]xe2x=12xe2xsin(2x)−(14x2−38)e2xcos(2x)
y=C1e2x+C2xe2x+12xe2xsin(2x)−(14x2−38)e2xcos(2x)
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