微分方程y3y”-1=0 求通解
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1个回答

  • 设y'=p,则y''=pdp/dy

    代入原方程得y³pdp/dy-1=0

    ==>y³pdp/dy=1

    ==>pdp=dy/y³

    ==>p²/2=-1/(2y²)+C1/2 (C1是积分常数)

    ==>p²=C1-1/y²

    ==>p=±√(C1-1/y²)

    ==>dy/dx=±√(C1y²-1)/y

    ==>ydy/√(C1y²-1)=±dx

    ==>d(C1y²-1)/√(C1y²-1)=±2C1dx

    ==>2√(C1y²-1)=±2C1x+2C2 (C2是积分常数)

    ==>√(C1y²-1)=±C1x+C2

    ==>C1y²-1=(C2±C1x)²

    ==>C1y²=(C2±C1x)²+1

    故原微分方程的通解是 C1y²=(C2±C1x)²+1 (C1,C2是积分常数)