XAC DI.NH HANG S^O Α SAO CHO Y=EΑX2 LA M^O.T NGHI^E.M RI^ENG CU'A...
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Xac di.nh hang s^o
αsao cho
y=eαx
2
la m^o.t nghi^e.m ri^eng cu'a phu.o.ng trnh vi ph^an:
y” + 4xy0
+ (4x2
+ 2)y= 0. Tm nghi^e.m t^o'ng quat cu'a phu.o.ng trnh ^ay.
HD gia’i:Ta tm nghi^e.m ri^eng du.o.i da.ng
y=eαx
2
thay vao du.o..c
α=−1va nghi^e.m
ri^eng
y1
=e−x
2
Nghi^e.m thu. hai:
y2
=y1
R y12
e−
R
P
(x)dx
dx=e−x
2
Re2x
2
e−
R
4xdx
dx=xe−x
2
.
1
V^a.y NTQ:
y=C1
e−x
2
+C2
xe−x
2