1.

Solve the differential equation:(D2 + 4D + 1)y = sin x .

Answer»

(D2 + 4D + 1)y = sin x

It's auxiliary equation is

m2 + 4m + 1 = 0

= m2 + 4m + 4 - 4 + 1 = 0

= (m + 2)2 = 3

= m + 2 = ± √3

= m = -2 ± √3

C.F = C1e-(2 + √3)x + C2e-(2 - √3)x

P.I = \(\cfrac1{D^2+4D+1}\) sin x

\(\cfrac1{-1^2+4D+1}\)sin x

\(\cfrac1{4D}\) sin x

\(\cfrac1{4}\) \(\int\) sin x (\(\because\) \(\cfrac1{D}\) f(x) = \(\int\) f(x) )

= - \(\cfrac1{4}\) cos x

\(\therefore\) complete solution of given differential equation is

y = C.F + P.I

= C1e-(2 + √3)x + C2e-(2 - √3)x

\(\cfrac{-cos\,x}4\)



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