View Full Version : Partial Fraction
Big Toosie
Dec 20, 2006, 11:16 AM
I have work this problem (1/P)dP/dt=b+aP to the point that I am confused on the partial fraction part
(1/P)dP/dt=b+aP
1/dt=bP+aP^2/dp this where Iam stuck to finish the equation I must do partial fraction.:eek:
asterisk_man
Dec 20, 2006, 12:34 PM
Can you state the original problem? What are you trying to solve for?
Is your dP/dt implying a derivative?
I assume it must because otherwise your left hand side the d/d and the P/P would cancel to give 1/t
But then I'm still confused because you're taking the derivative of P with respect to t... but you don't have any t anywhere.
More info on the problem will help us help you... unless someone comes by and tells me I'm an idiot... which is possible!
Big Toosie
Dec 20, 2006, 03:20 PM
The Original Problem is
1/P dP/dt=b+aP <<Edit by capuchin, you didnt mean to put the ^2 here right?
Now multiplying P to both sides gives
dP/dt=bP+aP^2
Now dividing by dP to get dt on one and dP on one side
1/dt=(bP+aP^2)/dp
This where I am suck I have to use Partial fraction to finish the problem.
Capuchin
Dec 20, 2006, 06:12 PM
Why do you move the dp over?
Why don't you integrate wrt t?
asterisk_man
Dec 20, 2006, 07:04 PM
but that's where I'm confused. Since there isn't any t in the equation bP+aP^2 is a constant so just replace it with C and you've got dP/dt=C and the integral is P=Ct=(bP+aP^2)t
then I guess you can solve for P if you'd like
P/(P(b+aP))=t
1/(b+aP)=t
b+aP=t
aP=t-b
P=(t-b)/a
but I'm just saying this because I'm not sure where else to go with this
malijfar
Dec 9, 2008, 06:55 PM
Gerald and Michelle went on a 24-mile bike ride. By lunchtime, they had ridden 5/8 of the total distance. How many miles did they have left to ride after lunch?
galactus
Dec 10, 2008, 03:45 PM
This is a logistic equation.
\frac{dP}{dt}=P(b+aP)
Separate and take partial fractions:
\frac{dP}{P(a+bP)}=dt
\left(\frac{\frac{1}{b}}{P}-\frac{\frac{a}{b}}{b+aP}\right)dP=dt
Integrate:
\frac{1}{b}ln|P|-\frac{1}{b}ln|b+aP|=t+c
Multiply both sides by b and use law of logs
ln|\frac{P}{b+aP}|=bt+bc
Now, can you finish?