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View Full Version : Differential Equations - I need Help

KneeGrow
03-28-2004, 07:52 PM
Okay here's a few problems that i've solved, i just need some math wiz to check me on my work. Thanks a lot guys, i really appreciate it!

1. y''' - 4y'' + y' + 6y =0
ANSWER: y=(c1)e^(3X) + (c2)e^(2X) + (c3)e^(-X)

2. 4y''' + 28'' + 61y' + 37y =0
ANSWER: y=(c1)e^(-X) + (c2)e^(-3X)(cos0.5X) + (c3)e^(-3X)(sin0.5X)

3.y'''' - 2y''' + 2y'' -2y' + y =0
ANSWER: y=((c1) + c(2)X)e^X + (c3)e^X(cosX) + (c4)e^X(sinX)

4. 4y''''' - 23 y'''' -33y'' - 17y' - 3y =0
ANSWER: y=(c1)e^(3X) + ((c2) + (c3)X)e^(-X) + ((c4) + (c5)X)e^(-0.5X)

FOR # 5/6 I USED METHOD OF UNDETERMINED COEFIFICENTS FOR NONHOMOGENEOUS DIFF EQ'S

5.y'' - 3y' - 4y = 2sinX
ANSWER: y=(c1)e^(4X) + (c2)e^(-X) + (3/17)cosX - (5/17)sinX

6.y'' - 3y' -4y = 4X^2
ANSWER: y= (c1)e^(4X) + (c2)e^(-X) - (1/8) - (1/4)X^2

Xterria
03-28-2004, 08:23 PM
I hope i never have to do math that hard...

axon
03-28-2004, 08:28 PM
>>I hope i never have to do math that hard...

well if you are going into ANY engineering field you will have to leardn DFQ. KneeGrow, I'll check it out later tonite if I get some spare time.

Xterria
03-28-2004, 09:08 PM
-DAAWEETED!!!!!!-

golfinguy4
03-28-2004, 09:11 PM
You are a loser.

Xterria
03-28-2004, 09:26 PM
huh? what'd i do now?
EDIT
alright i get it..
..i guess ill delete it

axon
03-28-2004, 09:36 PM
I obviously missed something

KneeGrow
03-28-2004, 09:37 PM
Ahh someone please check those answers the first four are so easy just check for the roots then do e^x but i need someone to check 5 + 6

Thanks a lot

Aran
03-28-2004, 11:10 PM
agh.... type in sentences please :)

I only WISH i could do those problems. I guess you just aren't an english person.

[half j/k]
And, also, your cheap attempt at making it look like you have 4000 something posts is, at the very least, laughable and embarassing. Embarassing not only to you, but to all of mankind (for harboring such rabid stupidity!). :D
[/half j/k]

KneeGrow
03-28-2004, 11:30 PM
Okay whatever ya'll can stop posting on this thread as i have figured out all the answers Thanks to all that helped = 0 people lol? Anyways whatever