GIA'I PHU.O.NG TRNH
123)
Gia'i phu.o.ng trnh:
y” +y= sinx+ cos 2xHD gia’i:Phu.o.ng trnh da.c tru.ng
λ2
+ 1 = 0⇔λ=±iNghi^e.m t^o'ng quat cu'a phu.o.ng trnh thu^an nh^at:
y=C1
cosx+C2
sinx.Tm nghi^e.m ri^eng da.ng:
y=x(Acosx+Bsinx) +Ccos 2x+Dsin 2xThay vao phu.o.ng trnh va d^ong nh^at du.o..c:
A=−12; B = 0; C =−13; D= 0V^a.y nghi^e.m t^o'ng quat:
y=C1
cosx+C2
sinx− 12xcosx−13cos 2x.