Math Is Fun Forum
You are not logged in.
- Topics: Active | Unanswered
#1 Re: Help Me ! » Laplace Transform Help Needed » 2007-07-17 12:11:23
I don't really understand the integration nor the point of it but I think this is the correct way to get the answer.
from 0 to a#2 Help Me ! » Laplace Transform Help Needed » 2007-07-15 06:49:54
- Old_Steve
- Replies: 1
The problem states that I should recall that
Assuming that the necessary elementary integration formulas extend to this case, find the Laplace transform of the given funtion; a and b are real contants.
The workbook states that I should use the formula for
to solve the problem.I'm totally lost on this one. Can anyone help?
#3 Re: Help Me ! » Sum of Power Series to Single Series » 2007-06-18 10:55:02
I guess the goal is to turn the DE into a power series equation, combine the series and solve for the coeff but my Calculus is weak. Especially in the sereis area.
#4 Re: Help Me ! » Sum of Power Series to Single Series » 2007-06-18 10:48:08
Thanks but I should be able to substitute the power series into the DE and solve for the coefficeints.
I'm having a hard time solving for the coeff.
I have the following but I'm not sure its right.
This is where I get messed up if I haven't already. All coeff are supposed to be in terms of
and#5 Re: Help Me ! » Need help with DEs problems » 2007-06-16 23:50:17
Let C(t) = Salt concentration at any time t.
Let Q(t) = Amount of salt in the tank at time t.
C(t) = Q(t)/100
dQ/dt at which Q(t) changes is equal to rate in minus rate out. Rate in is 1/2 * 6 = 3lbs/min
Rate out is teh concentration out * rate drained. C(t)lbs/min * 4 gal/min
p(x)= 0.04 and g(x) = 0.03
At zero time C(0) = 10lbs/100gal = .1
solve
Hopefully, this will get you the right equation to plug in your time for t - 25min
#6 Help Me ! » Sum of Power Series to Single Series » 2007-06-16 12:23:24
- Old_Steve
- Replies: 3
I am having trouble reducing the following equation to a single series. I need to factor out the x variable to solve the diff. eq. by power series method. I appreciate any help anyone could offer! I struggle with series stuff.
The original diff. eq. is
I usedThis latex stuff is nice!
Thanks again!
#7 Re: Help Me ! » TI-89 - Wronskian » 2007-05-29 13:00:57
Any ideas?
#8 Re: Help Me ! » Diff Eq. Confusion » 2007-05-29 12:59:35
Actually, I submitted the work. I'll compare with my answer when get it back.. Thanks for your help.
#9 Help Me ! » TI-89 - Wronskian » 2007-05-27 05:57:56
- Old_Steve
- Replies: 2
Can a Ti-89 solve 2x2 and 3x3 Wronskian?
#10 Re: Help Me ! » Diff Eq. Confusion » 2007-05-27 05:55:51
Thanks Harman.
#11 Re: Help Me ! » Can't get it - Diff Eq. Problem » 2007-05-26 07:55:47
Makes sense.
#12 Re: Help Me ! » Can't get it - Diff Eq. Problem » 2007-05-26 05:28:50
I hate to be ignorant but I don't really follow the first line. And, I missed how y=C.
Can you point me in the right direction. I need to get this down or I will never make it.
Thanks.
#13 Help Me ! » Can't get it - Diff Eq. Problem » 2007-05-26 01:04:07
- Old_Steve
- Replies: 4
y" + y*(y')^3 = 0
Let v = y' therfore v'= f(y.v) which uses variables x, y & z eliminate x by thinking of y as independent via chain rule v*(dv/dy) = f(y.v) There will be two constants in the final result
I having trouble setting up and solving.
Thanks for any help.
#14 Re: Help Me ! » Second order Diff Eq. Solved by Subsitution leading to First Order » 2007-05-26 00:58:29
I see it. Thanks George.
#15 Help Me ! » Your Equations in a post » 2007-05-24 11:53:45
- Old_Steve
- Replies: 2
How do you all get the equations to look so nice?
#16 Help Me ! » Second order Diff Eq. Solved by Subsitution leading to First Order » 2007-05-24 11:50:11
- Old_Steve
- Replies: 5
I have a problem that I need to make subsitutions leading to first order.
x^2*y"+2*x*y'-1=0 substituting v=y' and v'=y" it becomes the first order equation x^2*v'+2*x*v-1=0
I can solve the first order via a general solution formula for a first order linear equation. The answer for first order is v= (1/x) + (c/x^2)
I can figure out how to get back to an answer for the original second order for an answer using this required method. I'm sure it has something to do with my rusty Calculus skills.
Can anyone figure the problem via this method? Thanks so much!
#17 Re: Help Me ! » Diff Eq. Confusion » 2007-05-24 11:38:50
Thanks! You make it look easy!
#18 Help Me ! » Diff Eq. Confusion » 2007-05-23 11:34:23
- Old_Steve
- Replies: 7
I supposed to decide if the following are linear, non-linear, seperable, exact, homogeneous or one that requires and integrating factor:
(x)dy-(y)dx = ((x*y)^(1/2))dx and (x)dy-(y)dx =(2x^2*y^2)dy
Of course, non of the examples show an equation set up like this two. Can anyone help arrange it so I can decide? Thanks in advance!
#19 Re: Help Me ! » Non-Linear Diff. Eq. - Help! » 2007-05-21 13:07:04
Thanks for explaining.
#20 Re: Help Me ! » Non-Linear Diff. Eq. - Help! » 2007-05-21 10:18:34
Can you tell me why C must be ln(C) at the end? Why when you integrate is it not just + C?
I have other problems I am working that will only work when C = ln(C)
#21 Re: Help Me ! » Differential Equation Help » 2007-05-21 08:21:57
Yes! It should have been g(y). I was able to solve it as a first order linear diff eq. with u(y)=e^-y. Multiply through and integrate. Then multiply trough again and the answer is x = e^y[y +c].
#22 Re: Help Me ! » Differential Equation Help » 2007-05-20 22:07:49
I actually had to go back and work it as a first order equation. It fits the form x' + p(y)x = g(x). I would enter my work but I don't know where you all get your fomula editors. Anyway, I was able to arrive at the correct answer by working it as a firt order equation.
#23 Re: Help Me ! » Non-Linear Diff. Eq. - Help! » 2007-05-20 22:03:51
Thanks! I had more problems with the algeraic conversion at line 2 than anything.
#24 Help Me ! » Non-Linear Diff. Eq. - Help! » 2007-05-20 13:04:14
- Old_Steve
- Replies: 5
It seems they make all the examples in the books easy. Here is a first order diff. eq that I need to solve:
(3y^2 + 2xy)dx - (2xy+x^2)dy = 0
I appreciate any help!
Answer is (y^2/x^3)+(y/x^2)=c but I can't seem to get there.
#25 Re: Help Me ! » Differential Equation Help » 2007-05-16 10:47:38
Well...unfortunately you lost me. 
We have not started second order differential equations yet and I don't think I am supposed to solve it that way. I'll keep trying. Thanks for your help!!!!