The differential equation of the ellipse with centre at origin and ends of one axes of symmetry at ±1,0 is
x2−1y1−xy=0
x2+1y1−xy=0
xy1+x2+1y=0
x2−1y11+x-1y1=0
Let the ends of other axis of symmetry be 0,±a . Then the equation of the ellipse is x2+y2a2=1
→a2x2+y2=a2......(1) Dwr to x→2a2x+2yy1=0→a2=−yxdydx.......(2) From 1 and 2⇒x2−1dydx−xy=0 .