1.y^2-2xy+9=0
2yy'-2(xy'+y)=0
y'=y/(y-x)
2.
x'(t)=-Asint
y'(t)=Acost
dy/dx=y'(t)/x'(t)=-cott
d(dy/dx)/dt=(csct)^2
d^2y/dx^2=(csct)^2/(-Asint)
=-(csct)3/A