Solving the time-differential equation: I want to solve \(\displaystyle\ddot{{{y}}}={y}{\exp{{\left({t}\right)}}}\) with

avalg10o

avalg10o

Answered question

2022-04-02

Solving the time-differential equation:
I want to solve
y¨=yexp(t)
with the initial conditions y(0)=0, and y(1)=0.
How would I even go about doing this?

Answer & Explanation

Gia Edwards

Gia Edwards

Beginner2022-04-03Added 12 answers

Step 1
Denote:
y(t)=nantn
then
y˙(t)=nnantn1,
y¨(t)=nn(n1)antn2
=n(n+2)(n+1)an+2tn
On the other hand
y(t)exp(t)=nantnm1m!tm
=nk=0nak(nk)!tn
If we compare the coefficients, we get
2a2=a0
6a3=a0+a1
12a4=12a0+a1+a2

The initial conditions give us a0=0 and nan=0. The formulae above gives us, that the sign of a1 determines the signs of all an. That is nan=0 is only possible for a1=0 But then (by induction) and the above an=0 for all n. Hence y=0
kaosimqu5t

kaosimqu5t

Beginner2022-04-04Added 10 answers

Step 1
y¨=yexp(t)
Change the vaiable uet the DE becomes:
uy+yy=0
With initial conditions:
y(1)=0
y(e)=0
Then solve with a series soluton.
y(u)=n=0aνn

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