Find the center of the circle using the circumscribing the circle method.

Step 1:

Draw the square outside the circle in such a way that each of the four sides touches the circle

at only one point.

The line touches the circle at and . 

The square thus formed is .

Step 2:

Join the opposite vertices of the square which forms the diagonals of the square.

The diagonals such formed are and .

Step 3:

The intersection point of these two diagonals is required center .

Above steps are illustrated in the figure.