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Can someone help me with a differential equation?

Hello,

How can I find the general solution to this equation?

dy/dx = y^2(4 - y^2)

I have several in a similar format to solve. I'm a little stumped :(

Update:

Thank you Eric, I did actually get that far, but then I wasn't sure how to integrate it. I can't picture how to end up with y=something. :(

4 Answers

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  • 1 decade ago
    Favorite Answer

    dy/dx = y^2(4-y^2)

    dy/dx = 4y^2-y^4

    dy * ( 1 / (4y^2-y^4) ) = dx

    integrate both sides. Left side is not simple. I looked it up on wolframs integrals.com

    (-y*log(y-2) - y * log(y+2) + 4 ) / (16* y) = x

    solving for y looks difficult.

    There might be a way using the something similar to the method of undetermined coefficients, but that is used for solving a linear differential equation.

  • 1 decade ago

    You can integrate 1/(y^2(4-y^2)) by partial fractions.

    First factor the denomiator:

    1/(y^2(2-y)(2+y)), then

    solve for A, B C, and D:

    (Ay+B)/y^2 + C/(2-y) + D/(2+y) = 1/(y^2(2-y)(2+y))

    When you solve this, you get A=0, B=1/4, C=D=1/16.

    This gives you three integrals that you can evaluate.

  • ?
    Lv 6
    1 decade ago

    Are we trying to integrate 4y^2 - y^4?

    I think it's

    (4y^3) / 3 - (y^5) / 5 + C

  • 1 decade ago

    maybe this will help...

    [1/(4y^2 - y^4)]dy = dx

    annnnnd integrate

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