# Another complex r00ts 2nd ODE! gahh! i <3 DiffEQ

1. Feb 17, 2006

### mr_coffee

Look whos back! I ran into another problem, i redid the problem twice and i keep coming out with the same answer!
here is what i have:

This is waht I submitted which was wrong:

This is what
Thanks!

Last edited by a moderator: Apr 22, 2017
2. Feb 17, 2006

### Pseudo Statistic

If you're having trouble doing it with sine and cosine, do it the old fashioned Ae^r1x + Be^r2x way using the complex roots. (It's an alternative method and chances are you'll make less mistakes)

3. Feb 17, 2006

### HallsofIvy

Staff Emeritus
If that is what you actually submitted, you might want to compare it closely to your handwritten answer- do you notice some missing parentheses?

4. Feb 17, 2006

### mr_coffee

Pseudo, this program that evaluates the expressions tells us to not use that form becuase it won't evaluate complex expressions inside the e^, so I have to use sin/cos. :(

Thanks i didn't catch that halls but it still told me, do not pass go, do not collect 200 dollars. I think i shall e-mail the professor and see if its corrrect and the program might just b f'ed up.

Last edited by a moderator: Apr 22, 2017
5. Feb 17, 2006

### assyrian_77

Again, like last time, your differentiation is wrong! You seem to forget that there is a fraction in the exponential; your didn't include the denominator (1000) in the differentiation! It is the exact same mistake you did last time. I suggest you carefully go through the differentiation again.

Last edited: Feb 17, 2006
6. Feb 17, 2006

### mr_coffee

Okay i redid it, i'm not sure if its right t hough becuase the webhomeworks happen to be down. but this is what I got:

Last edited by a moderator: Apr 22, 2017
7. Feb 17, 2006

### assyrian_77

I ended up with the equation

$$7=\frac{14}{1000}-\frac{\sqrt{2951}}{1000}B$$

so B should be

$$B=-\frac{6896}{\sqrt{2951}}$$

However, I could have made a mistake.

8. Feb 18, 2006

### mr_coffee

Hm...I tried my answer and your answer, switching the signs as well but can't seem to get it right.

Last edited by a moderator: Apr 22, 2017