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Math Help - Strange Differental Equation Pls Help

  1. #1
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    Strange Differental Equation Pls Help

    Please help to solve the nonhomogenious side of this differential equation.

    so the equation is y"+4y'+4y=25*sinX

    can't solve the equation after putting back of the first and the second derive of the probe function.

    And the probe function is: y=A*sinX+B*cosX+C
    First derive: y'=A*cosX-B*sinX
    Second derive: y"=-A*sinX-B*cosX

    If you put it back its gonna be a huge mess

    Pls Help
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  2. #2
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    Quote Originally Posted by gergofoto View Post
    Please help to solve the nonhomogenious side of this differential equation.

    so the equation is y"+4y'+4y=25*sinX

    can't solve the equation after putting back of the first and the second derive of the probe function.

    And the probe function is: y=A*sinX+B*cosX+C
    First derive: y'=A*cosX-B*sinX
    Second derive: y"=-A*sinX-B*cosX

    If you put it back its gonna be a huge mess

    Pls Help
    Plugging in:

    -A \sin{x} - B \cos{x} + 4 A \cos{x} - 4 B \sin{x} + 4 A \sin{x} + 4 B \cos{x} = 25 \sin{x}

    (3A - 4B) \sin{x} + (4A + 3B) \cos{x} = 25 \sin{x}

    Now just compare coefficients.
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