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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

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  • 10 years ago
    Favorite 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)

  • Indica
    Lv 7
    10 years ago

    (1−x²)dy/dx − x²y = (1+x)√(1−x²)

    Divide by 1−x² : dy/dx − {x²/(1−x²)}y = √{(1+x)/(1−x)} … (i)

    IF is exp{ ∫ −{x²/(1−x²)}dx }

    ∫ {x²/(1−x²)}dx = ∫ { 1/(1−x²) − 1 }dx = ∫ { ½/(1+x) + ½/(1−x) − 1 } dx

    = ½log(1+x) − ½log(1−x) − x = ½log{(1+x)/(1−x)} − x

    â��´ IF = exp{ x−½log{(1+x)/(1−x)} } = exp(x)*√{(1−x)/(1+x)}

    Multiplying (i) by IF, noting that the LHS is always d( IF*y )/dx

    d( y*exp(x)*√{(1−x)/(1+x)} )/dx = exp(x)

    Integrating : y*exp(x)*√{(1−x)/(1+x)} = exp(x) + c

    ∴ y = √{(1+x)/(1−x)} * (1+cexp(−x) )

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