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First order linear differential equations help?

How do I solve this differential equation using the first order linear differential equations?

dy + 3ydx = e^(-3x) dx

3 Answers

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  • cidyah
    Lv 7
    10 years ago
    Favourite answer

    divide by dx

    dy/dx + 3y = e^(-3x) -----------(1)

    Equation of the form dy/dx +yp(x)=q(x)

    p(x)=3

    q(x)=e^(-3x)

    Compute the integrating factor e^∫p(x) dx = e^∫3 dx = e^(3x)

    Multiply both sides of (1) by the integraing factor e^(3x)

    e^(3x) dy/dx + 3y e^(3x) = e^(-3x)e^(3x)

    e^(3x) dy/dx + 3y e^(3x) = 1 --------(2)

    The left side of (2) is the derivative of ye^(3x) or [ye^(3x)]'

    (2) may be written as

    [ye^(3x)] ' = 1

    Integrate both sides

    ∫[ye^(3x)] ' = ∫ 1 dx

    y e^(3x) = x + C

    divide both sides by e^(3x)

    y = x e^(-3x) + C e^(-3x)

  • 10 years ago

    Lol so easy

    jst divide by dy

    u wil get

    1 + 3y (dx/dy) =e^(-3x) (dx/dy)

    nw after arranging

    (e^(-3x) - 3y ) (dx/dy) = 1

    nw

    dx/dy = (1 / (whole thing) )

    this is simplified and i hope u can solve next steps

  • Anonymous
    5 years ago

    2(dy/dx) = 5 - 6y This is actually seperable: dy/(5 - 6y) = dx/x Integrating both sides: -1/6*ln|5 - 6y| = ln|x| + C solve for y.

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