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Separation of variables: dy/dx = 4x + y?

Help please!

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  • 9 years ago
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    This is not a separable differential equation so it cannot be solved that way.

    Rewrite this differential equation in standard form:

    dy / dx = 4x + y

    dy / dx - y = 4x

    Find the complementary function by solving the auxiliary equation:

    dy / dx - y = 0

    m - 1 = 0

    m = 1

    yᶜ = C℮˟

    Find the particular integral by comparing coefficients:

    yᵖ = Ax + B

    dyᵖ / dx = A

    dyᵖ / dx - yᵖ = 4x

    A - (Ax + B) = 4x

    A - Ax - B = 4x

    (A - B) - Ax = 4x

    -A = 4

    A = -4

    A - B = 0

    B = A

    B = -4

    yᵖ = -4x - 4

    Find the general solution by combining these two parts:

    y = yᶜ + yᵖ

    y = C℮˟ - 4x - 4

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