Suppose you are given a circle. Give a construction to find its centre.

Explanation

let the points on the circle as described in figure as P, Q & R

join PQ & QR

draw 2 `_|_` CS to the line PQ & CT to the line respectively

S & T are midpoints of PQ & QR

draw a line from point S & T

which is `_|_` to line PQ & QR

inter section point of lines is centre of circle

thus we can get the centre