令y'=p，y"=pdp/dypdp/dy+1/y^3=0p^2-1/y^2=c当x=1 时，y=1,y'=0,c=-1p=±√(1-y^2)/y±ydy/√(1-y^2)=dx±√(1-y^2)=x+c1当x=1 时，y=1,c1=-1(x-1)^2+y^2=1
