[b]How do you find the centre of a rotation? [/b][br]We can use the property that "[i]a radius perpendicular to a chord bisects the chord[/i]". Hence, the perpendicular bisector of a chord will pass through the centre of the circle. Where on the perpendicular bisector? If we just have one chord, we don't know. The solution is to bisect another chord. The point where the perpendicular bisectors intersect must be the centre of the circle.[br][list][*]Play the construction protocol to learn more.[/*][*]The centre of rotation, O, can be dragged.[/*][*]The centre of rotation, O, can be shown or hidden.[/*][*]The angle of rotation can be adjusted with the slider.[/*][/list]