The order of rotational symmetry for an equilateral traingle is 3. It says in the study material that "If we rotate the triangle about the centre of rotation through an angle of 120 then a similar shape will be obtained." But why120? How come we know we have to rotate the equilateral triangle120 each time to retain its orginal position? Why can't we rotate it by 90 degrees rather? Please answer! Thank you :D