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