How do you find radius of a circle?

Answer 1

Draw a line from any part on the outside of a circle to the exact center of the circle.

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That is fine if you know where the center is but not much use if you are just given a circle and do not know where the exact centre is. In this case:

Draw a chord - a straight line joining any two points on the circumference of the circle. Then draw the perpendicular bisector of the chord.

Draw another chord and its perpendicular bisector. The two perpendicular bisectors will meet at the centre.