Re: Integrating Factor error

Quote:

Originally Posted by

**astuart** Hello,

Could someone point out where I'm going wrong here - I'm making a mistake somewhere, and it's not clear to me what I'm doing wrong...

$\displaystyle \frac{dy}{dt}(t) - 3y +2 = 0$

$\displaystyle = \frac {dy}{dt} - \frac {3y}{t} = \frac {-2}{t}$

$\displaystyle I(t)=e^{\int \frac {-3}{t}}$

$\displaystyle =I(t) = e^{-3lnt} = t^{-3}$

$\displaystyle = \frac {dy}{dt}\cdot t^{-3} \frac {-3y}{t}\cdot t^{-3} = \frac {-2}{t} \cdot t^{-3}$

$\displaystyle = \int \frac {d}{dt}t^{-3}y = \int \frac {-2}{t^4}$

$\displaystyle = yt^{-3} = -2 \int t^{-4}$

$\displaystyle = yt^{-3} = -2 \frac {t^{-3}}{-3}+C$

$\displaystyle = yt^{-3} = \frac {2}{3} t^{-3}+C = \frac {2}{3t^3}+C$

$\displaystyle = y = \frac {2}{3} + C$

Now, I end up cancelling the t-value out, which can't be right. What am I doing wrong exactly?

Ahh, god, I think I can already see where I went wrong....

$\displaystyle y = \frac {2}{3} + Ct^3$