求微分方程xy''-y'=x^2e^x的通解
(xy''-y')/x²=e^x==>(y'/x)'=e^x==>y'/x=e^x+2C1 (C1是积分常"}}}'>

2个回答

  • 解法一:∵xy''-y'=x²e^x ==>(xy''-y')/x²=e^x

    ==>(y'/x)'=e^x

    ==>y'/x=e^x+2C1 (C1是积分常数)

    ==>y'=xe^x+2C1x

    ==>y=xe^x-e^x+C1x²+C2 (C2是积分常数)

    ∴原方程的通解是y=xe^x-e^x+C1x²+C2 (C1,C2是积分常数).

    解法二:∵令y'=p,则y''=p'

    ∴代入原方程,得xp'-p=x²e^x.(1)

    显然,齐次方程xp'-p=0的通解是p=Cx (C是积分常数)

    于是,根据常数变易法,设方程(1)的解为p=C(x)x (C(x)是关于x的函数)

    ∵代入方程(1),得x[C'(x)x-C(x)]-C(x)x=x²e^x

    ==>C'(x)=e^x

    ==>C(x)=e^x+2C1 (C1是积分常数)

    ==>p=xe^x+2C1x

    则方程(1)的通解是p=xe^x+2C1x (C1是积分常数)

    ∴y'=xe^x+2C1x ==>y=xe^x-e^x+C1x²+C2 (C2是积分常数)

    故原方程的通解是y=xe^x-e^x+C1x²+C2 (C1,C2是积分常数).