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need help with exact differential equation?
I need to solve (1-x^2)dy/dx-x^2y = (1+x)sqrt(1-x^2)
I am having plenty of trouble unfortunately. I have some work here. I'm pretty sure I went wrong somewhere, just cant find it.
Here is my work on google docs, you don't need to sign in or anything to view it.
https://docs.google.com/viewer?a=v&pid=explorer&ch...
me=true&srcid=0B1bnMNmwLoTc
YTc0N2Q4ZDgtMTA1My00ODJiLThjZWMtMmViMj
Q5ZTFhZjJm&hl=en_US
Just copy/paste
2 Answers
- RapidfireLv 710 years agoFavorite Answer
Solve this differential equation by using an integrating factor:
(1 - x²)(dy / dx) - x²y = (1 + x)√(1 - x²)
dy / dx - x²y / (1 - x²) = (1 + x) / √(1 - x²)
dy / dx + x²y / (x² - 1) = (1 + x) / √(1 - x²)
P(x) = x² / (x² - 1)
f(x) = (1 + x) / √(1 - x²)
I(x) = ℮^[∫ P(x) dx]
I(x) = ℮^[∫ x² / (x² - 1) dx]
I(x) = ℮^[∫ {1 - 1 / (1 - x²)} dx]
I(x) = ℮^(x - tanhˉ¹x)
I(x)y = ∫ I(x)f(x) dx
y℮^(x - tanhˉ¹x) = ∫ (1 + x)℮^[x - tanhˉ¹x] / √(1 - x²) dx
y℮^(x - tanhˉ¹x) = ∫ ℮˟ dx
y℮^(x - tanhˉ¹x) = ℮˟ + C
y℮^(x - tanhˉ¹x) = C + ℮˟
y = (C + ℮˟) / ℮^(x - tanhˉ¹x)
- IndicaLv 710 years ago
(1âx²)dy/dx â x²y = (1+x)â(1âx²)
Divide by 1âx² : dy/dx â {x²/(1âx²)}y = â{(1+x)/(1âx)} … (i)
IF is exp{ â« â{x²/(1âx²)}dx }
â« {x²/(1âx²)}dx = â« { 1/(1âx²) â 1 }dx = â« { ½/(1+x) + ½/(1âx) â 1 } dx
= ½log(1+x) â ½log(1âx) â x = ½log{(1+x)/(1âx)} â x
â��´ IF = exp{ xâ½log{(1+x)/(1âx)} } = exp(x)*â{(1âx)/(1+x)}
Multiplying (i) by IF, noting that the LHS is always d( IF*y )/dx
d( y*exp(x)*â{(1âx)/(1+x)} )/dx = exp(x)
Integrating : y*exp(x)*â{(1âx)/(1+x)} = exp(x) + c
â´ y = â{(1+x)/(1âx)} * (1+cexp(âx) )