# Homework Help: Solve ODE y''-y=e^{-t}

1. Nov 26, 2011

### matematikuvol

1. The problem statement, all variables and given/known data
Solve ODE
$$y''-y=e^{-t}$$

$$y(0)=1, y'(0)=0$$

2. Relevant equations

3. The attempt at a solution
Homogenuous solution

$$t^2-1=0$$

$$y=C_1e^t+C_2e^{-t}$$

From

$$y(0)=1, y'(0)=0$$

$$y=\frac{1}{2}e^t+\frac{1}{2}e^{-t}$$

How from that get complete solution?

2. Nov 26, 2011

### hunt_mat

Re: Ode

It's wrong. What you have to do it write:
$$y=C_{1}e^{t}+C_{2}e^{-t}$$
and then find the particular integral, call it $f(x)$ say, and then apply the boundary condition to the function:
$$y=C_{1}e^{t}+C_{2}e^{-t}+f(x)$$

3. Nov 26, 2011

### matematikuvol

Re: Ode

How to find particular integral?

4. Nov 26, 2011

### hunt_mat

Re: Ode

I would look for a function
$$y=Ate^{-t}$$
and likewise.

5. Nov 26, 2011

### matematikuvol

Re: Ode

How do you know how to look for the function?

6. Nov 26, 2011

### matematikuvol

Re: Ode

How you choose form of particular solution?

7. Nov 26, 2011