**Form the differentiate equation of all circles which pass through origin and whose centres lie on y – axis.**

###### Answers:

It is given that circles pass through origin and their centres lie on y-axis.

Let (0,k) be the centre of the circle and radiud is k.

So, the equation of circle is

(x-0)^{2} + (y-k)^{2} = k^{2}

⇒ x^{2} + y^{2} – 2ky = 0 ….(i)

Differentiating w.r.t.x, we get