Solve the inital value problem by using Laplace transform: y''-5y'+6y=-8cos(t)-2sin(t), y(frac{pi}{2})=1 ,y'(frac{pi}{2})=0

Amari Flowers

Amari Flowers

Answered question

2020-11-09

Solve the inital value problem by using Laplace transform:
y5y+6y=8cos(t)2sin(t),y(π2)=1,y(π2)=0

Answer & Explanation

SchulzD

SchulzD

Skilled2020-11-10Added 83 answers

Solve the inital value problem by using Laplace transform
y5y+6y=8cos(t)2sin(t),y(π2)=1,y(π2)=0
Step 2
Consider:y5y+6y=8cos(t)2sin(t),y(π2)=1,y(π2)=0First noticed that the initial condition are not at t=0.We can applythe Laplace transform of derivative is to have the initial condition at t=0.
This mean that we will need to formulate the IVP in such a way thatthe initial condition are at t=0.
We need to change the variable t=η+π2η=tπ2
y(η+π2)5y(η+π2)+6y(η+π2)=8cos(η+π2)2sin(η+π2)
y(η+π2)5y(η+π2)+6y(η+π2)=8sin(η)2cos(η)(2)
We have, u(η)=y(η+π2)
By using chain rule,
u(η)=dudη=dydηdηdt=y(η+π2)
u(η)=dudη=dydηdηdt=y(η+π2)
Hence,the initial condition for u(η) as
u(0)=y(π2)=1 and u(0)=y(π2)=0
Step 3
Now,the equation (2) becomes
u(η)5u(η)+6u(η)=8sin(η)2cos(η)
Apply the Laplace transform on both sides,then
L{u(η)}5L{u(η)}+6L{u(η)}=8L{sin(η)}2L{cos(η)}
s2u(s)su(0)u(0)5su(s)u(0)+6u(s)=8(s2+1)2s(s2+1)
s2u(s)s5su(s)+5+6u(s)=8(s2+1)2s(s2+1)
(s2+1)u(s)=8(s2+1)2s(s2+1)+s5
u(s)=8(s2+1)22s(s2+1)2+s(s2+1

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