Solve y′=−x/yy' = -x/yy′=−x/y.
x2+y2=Cx^2 + y^2 = Cx2+y2=C
y=−x2/2+Cy = -x^2 / 2 + Cy=−x2/2+C
y=−xy = -xy=−x
x2−y2=Cx^2 - y^2 = Cx2−y2=C