YAM(ath)T

[duragezic]

I'm got one homework problem for differential equations that requires using variation of parameters on a third order DE. I don't get how to form the Wronskian's and corresponding u primes with a third order DE, and the book for the class is pretty much useless.


Ok, so the DE is y-triple prime + y-prime = tan x. I can form the Wronskian but not the 3 other Wronskians coressponding to the u primes or whatever.

 

[helpme]

I took Differential Equations back a couple years ago, I'll see if I can find my notes.

Which book do you have? Mine was pretty bad too.

 

[duragezic]

anyone?

 

[DrPizza]

Been 15 years since I last did that... too rusty.

 

[duragezic]

anyone at all?

 

[DrPizza]

I don't even have my old diff eq's book around. My most recent book deals with differential equations in an entirely different way... I've taken 2 undergrad courses in differential equations, and other than the name of the course, there were very few similarities.

 

[dym]

Originally posted by: duragezic
I'm got one homework problem for differential equations that requires using variation of parameters on a third order DE. I don't get how to form the Wronskian's and corresponding u primes with a third order DE, and the book for the class is pretty much useless.


Ok, so the DE is y-triple prime + y-prime = tan x. I can form the Wronskian but not the 3 other Wronskians coressponding to the u primes or whatever.

first you have to find the characteristic equation, which is r^3+r=0
thus, r=0, +-i.
then you have to find the general ofrm of y, which will be: y(t)=c1+c2*sin(t)+c3*cos(t)
therefore,
y1 will be 1
y2 will be sint
y3 will be cost

form wronskian determinant by the derivative of the y1, y2, y3

any further help, contact me at potoba2000 (YM!) or pm me

Dym