Use Laplace transforms to solve the initial value problems.y"+4y=2\delta(t-\pi), y(0)=1 , y'(0)=0

Phoebe

Phoebe

Answered question

2021-09-16

Use Laplace transforms to solve the initial value problems.
y"+4y=2δ(tπ),y(0)=1,y(0)=0

Answer & Explanation

AGRFTr

AGRFTr

Skilled2021-09-17Added 95 answers

We know that L{δ(tt0)}=est0
and L1{easF(s)}=f(ta)u(ta)
Now , given that, y"+4y=2δ(tπ);y(0)=1.y(0)=0
Taking Laplace transformation on both sides we get,
L{y"+4y}=2L{δ(tπ)}
L{y"}+4L{y}=2L{δ(tπ)}
sY(s)sy(0)y(0)+4y(s)=2eπs
s2Y(s)s0+4y(s)=2eπs[y(s)=L{y}]
y(s)[s2+4]=2eπs+s
y(s)=2eπss2+4+ss2+4
Now taking inverse Laplace transformation,
y(d)=L1{2eπss2+4}+L1{ss2+4}
y(d)=L1{eπs2s2+22}+L1{ss2+22}   (2)
Now, L1{eπs2s2+22}
Let, F(s)=2s2+22,  Then  f(t)=sin2t
f(tπ)=sin2(tπ)
L1{eπs2s2+22}=f(t2)u(ta)
=sin(2t2π)u(tπ)
=sin2(tπ)u(tπ)
and L1{ss2+22}=cos2t
From (2) we get
y(t)=sin2(tπ)u(tπ)+cos2t

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