Need help with Differential Equations

[fatryan 5,000+ posts]

Im trying to work on this problem in my book and I just cant get it right. Im following the notes I took in class, but I just end up with the nastiest looking integral in the world. Help is greatly appreciated.

Solve D.E. by using variation of parameters

(D^2 - 2D + 1)y = (e^(2x)) / ((e^x + 1)^2)

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[fatryan 5,000+ posts]

bump

 

[.::DuD3::. 10+ year member]

sorry you're a couple semesters ahead of me. looks like fun though.

 

[TIeclipseMOJO 10+ year member]

that looks foreign to me, and im enrolled in that class. maybe ill start going...

ive helped a few people with calc I,II and III questions on here but diff eq is some hard shit

 

[fatryan 5,000+ posts]

i actually find differential to be easier than calc 2 and 3. in fact my average in the class right now is an A, i just got a 98.5 on my last test. may not seem spectacular to someone used to pulling those grades, but i got a C in calc 2 and a D+ in calc 3, so im happy. i just dont get this section cause my dumbass teacher didnt do any examples or even go over this shit thoroughly. he just went over it real quick, now im lost. //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

also, book is useless, just a paperweight. i hope none of you are ausing "Elementary Differential Equations" 8th ed. by Rainville...absolutley the WORST textbook ive ever owned, hands down.

 

[UndercoverPunk 5,000+ posts]

Does your school not have a math lab of some sort?

 

[fatryan 5,000+ posts]

that looks foreign to me, and im enrolled in that class. maybe ill start going...
ive helped a few people with calc I,II and III questions on here but diff eq is some hard shit

btw, thats differential operators, real easy...D=d/dx...D^2=(d^2)/(dx^2)...and so forth. just another way to right it to manipulate equations

 

[GemaRastem 10+ year member]

hold on, let me think haha, just had diff eq last semester

 

[fatryan 5,000+ posts]

Does your school not have a math lab of some sort?

ha ha it does, but most everyone there doesnt know anything past calc 2 //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif same goes for physics lab (nothing past general physics). stupid school sux balls. this kid in my electricity & magnetism class tutored me a couple times at the beginning of the semester, and im sure hed help after E&M tomorrow, but unfortunatley this stuffs due b4 that //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

 

[fatryan 5,000+ posts]

hold on, let me think haha, just had diff eq last semester

//content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif//content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
it has something to due with substituting U and V for the constants, and i think i understand where to go with it, but when integrating the right side....its fvckin impossible ha ha ha. thinkin maybe im missin something. also, not sure how to do it when theres 3+ constants

 

[GemaRastem 10+ year member]

alright this is a really involved problem, basically left side of the equation is (D-1)^2 giving you y=c1e^1x+c2xe^1x+A, you get the A from the other side.

 

[fatryan 5,000+ posts]

alright this is a really involved problem, basically left side of the equation is (D-1)^2 giving you y=c1e^1x+c2xe^1x+A, you get the A from the other side.

//content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif where does this A business come from? i got the yc=c1e^1x+c2xe^1x...but thats just for the left hand side. then you need to sub U and V for c1 and c2 and solve for both U and V (integrating the right hand side), then plug them back into the original equation...the integration got me. or maybe im multiplying by the wrong thing to solve for U and V...

 

[GemaRastem 10+ year member]

then you get the derivative of the right side, and then the 2nd derivative, you can do that work I don't feel like doing it

 

[GemaRastem 10+ year member]

ok yeah, your professor has you do it the hard way, we were taught that way, and then we were taught this really easy way that I'm trying right now, where you get the differentials of the right side and do all this shit, it's a little longer, but the math is a lot less complicated

 

[GemaRastem 10+ year member]

I don't remember all the **** steps