Given that the circle passes through the points O(0,0), A(a,0) and B(0,b).

Let us first find the length of the sides of the triangle formed by the points OAB.

We know that distance between two points (x₁,y₁) and (x₂,y₂) is .

⇒

⇒

⇒ OA = |a| .....(1)

⇒

⇒

⇒ OB = |b| .....(2)

⇒

⇒ ..... (3)

Now consider OA² + OB²,

⇒ OA² + OB² = (|a|)² + (|b|)²

⇒ OA² + OB² = a² + b²

⇒

⇒ OA² + OB² = AB²

We got ABC is a right angled triangle with AB as the hypotenuse.

We know that the circumcentre of a right-angled triangle is the midpoint of the hypotenuse.

⇒ Centre =

⇒ Centre =

∴ The coordinates of the centre is .