(x – a)2 + (y – b)2 = r2 …… (i)
On differentiating with respect to x, we get,

Again, differentiating with respect to x we get,

Put the value of (y – b) obtained in (ii) we get,

Put the value of (x – a) and (y – b) in (i) we get,

So, the required differential equation is (y’3 + y’)2 + (y’2 + 1)2 = r2y’’2.