# Linear equation (differential equations) problem

1. Jan 20, 2013

### aero_zeppelin

1. The problem statement, all variables and given/known data

Solve:

dP/dt + 2tP = P + 4t - 2

3. The attempt at a solution

I've done a couple of these but I'm not sure how to start with this one...

First I have to put it in standard form right?

dP/dt + P(2t - 1) = 4t - 2

Then obtain the integrating factor by integrating (2t - 1)

2. Jan 20, 2013

### LCKurtz

Right so far. Now calculate$$e^{\int 2t-1 dt}$$for your integrating factor.

3. Jan 20, 2013

### aero_zeppelin

Ok! I get:

e^(t^2 - t)

Then we include it in the equation and integrate both sides?

d [e^(t^2 - t) P ] / dt = e^(t^2 - t) * (4t - 2)

The right hand side integral is giving me problems though...

4. Jan 20, 2013

### LCKurtz

Try a u substitution: $u = t^2-t$ as your first step.

5. Jan 20, 2013

### aero_zeppelin

Oh god, I can't believe I missed that one hehe I was overcomplicating it...

I end up with:

P = [2 e^(t^2 - t) + C ] / e^(t^2 - t)

Interval of definition would be (-inf, inf) correct?

6. Jan 20, 2013

### LCKurtz

Yes, since the denominator is never zero.

7. Jan 20, 2013

### aero_zeppelin

Thanks a lot!