Homework Help: 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:
http://img139.imageshack.us/img139/6205/lastscan5qw.jpg [Broken]
This is waht I submitted which was wrong:
http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/d3/290d3b430db500dfaef04358236c001.png [Broken]
This is what
Thanks!

Last edited by a moderator: May 2, 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

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.
http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/3d/4a14ab68c9143ae5c68ed8af6e5ba91.png [Broken]

Last edited by a moderator: May 2, 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:
http://img212.imageshack.us/img212/6735/lastscan1rm.jpg [Broken]

Last edited by a moderator: May 2, 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.
http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/02/a1ed9e2620a00e5df238eb7b1954831.png [Broken]

Last edited by a moderator: May 2, 2017