# Separable differential equation problem

• Sep 27th 2011, 08:45 AM
s3a
Separable differential equation problem
Could someone please take a look at "#6 (Again)" from the attached PDF file and tell me if something stands out as wrong because I keep getting the wrong answer? If you're lazy (or whatever the reason is) but you see my mistake(s), you don't have to explain to me how to do it but just tell me where the mistake(s) is/are and I will try to figure it out myself.

Any input would be greatly appreciated!
• Sep 27th 2011, 09:16 AM
Ackbeet
Re: Separable differential equation problem
Your problem isn't the initial solution, but in plugging in the initial condition. The equation

\$\displaystyle 0=C_{1}^{2}-6C_{1}+7\$ should be

\$\displaystyle 0=C_{1}^{2}-6C_{1}-7.\$

You tried too many steps at once in getting to that equation, and then forgot that you didn't actually flip the sign of the RHS.
• Sep 27th 2011, 01:05 PM
s3a
Re: Separable differential equation problem
I still get C1 = 3 +/- sqrt(2)

(The modified version - as of the step you corrected - of the previous PDF is attached).
• Sep 27th 2011, 01:14 PM
s3a
Re: Separable differential equation problem
I caught the last mistake I had. This time I had rooted the b^2 - 4ac part twice in the quadratic formula. Thanks.
• Sep 28th 2011, 01:54 AM
Ackbeet
Re: Separable differential equation problem
You're welcome! Have a good one.