Non-homogeneous ODE via Power Series

In summary, you are having trouble with the power series for the sine function and you need help figuring out what to do next.
  • #1
teddy_boo
8
0
Hey there! I'm new here and I just want to ask anyone willing how to solve this problem using power series:

y"+3y'+2y= sin x

y(0)=0
y'(0)=1

Evaluate y(0.1)

Thanks! :smile:
 
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  • #2
It is impossible to explain something like that without knowing what you already understand about differential equations and power series.

It would be better if you what you understand about this problem and where you have trouble. What have you tried?

(I suppose it would be tacky of me to suggest that this looks like a homework problem. You wouldn't do that, would you?)
 
  • #3
You are aware this can be solved analytically, yes? Just making sure.
 
  • #4
Yes, I'm aware it could be solved analytically. My problem lies with the fact that after having changed the entire expression into power series, I'm totally blank on what to do next. The power series for the sine function is complicated relative to the one for y and its derivatives. I'm looking for some way to enable the sine function to be workable. Do you have any hints at least? Or am I looking at an inappropriate way to solve the ODE?
 
  • #5
You say you have "changed the entire expression into power series". Please show what you have. The power series for sin x is relatively simple and I would like to see what exactly is giving you trouble. I suspect I know what your difficulty is but I don't want to go into a long-winded explanation if I am wrong.
 
  • #6
Okay, so here's the equation:

∑_(i=2)^∞▒〖i(i-1) a_i x^(i-2)+3∑_(i=1)^∞▒〖ia_i x^(i-1)+2∑_(i=0)^∞▒〖a_i x^i=∑_(i=0)^∞▒(〖(-1)〗^i x^(2i+1))/(2i+1)!〗〗〗
 
  • #7
Here's another way to put it upon expansion:

(2a_2+6a_3 x+12a_4 x^2+⋯)+(3a_1+6a_2 x+9a_3 x^2+⋯)+(2a_0+2a_1 x+2a_2 x^2+⋯)=x-x^3/3!+x^5/5!+⋯
 
  • #8
After expansion, I don't know how to factor x^3 and x^5 terms.
 
  • #9
Oh, everything's okay now, I was able to get the answer. Haha, I'm an idiot. My problem's easily remedied by just expanding the series further. Thanks anyway :smile:
 

FAQ: Non-homogeneous ODE via Power Series

1. What is a non-homogeneous ODE?

A non-homogeneous ODE (ordinary differential equation) is a type of differential equation where the dependent variable and its derivatives are not equal to zero. This means that the solution to the equation will not be a linear combination of basic solutions.

2. What is a power series?

A power series is a representation of a function as an infinite sum of terms, each of which is a polynomial multiplied by a variable raised to a different power. In other words, it is an expression of the form a0 + a1x + a2x2 + ... + anxn, where the coefficients an are constants and x is the variable.

3. How do you solve a non-homogeneous ODE via power series?

To solve a non-homogeneous ODE via power series, we first assume that the solution can be expressed as a power series. Then, we substitute this series into the equation and equate coefficients of like powers of the variable. By solving for the coefficients, we can find the general solution to the non-homogeneous ODE.

4. When is it appropriate to use power series to solve a non-homogeneous ODE?

Power series are typically used to solve non-homogeneous ODEs when the coefficients in the equation are constant and the function or its derivatives are difficult to integrate directly. Power series can also be useful when the function has a singularity or when the initial conditions are not specified.

5. What are some applications of solving non-homogeneous ODEs via power series?

Power series can be used to solve a wide range of problems in physics, engineering, economics, and other fields. Examples include modeling population growth, predicting the behavior of electrical circuits, and analyzing the motion of objects under the influence of forces. Power series solutions can also be used to approximate the solutions to more complex differential equations.

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