The order of rotational symmetry is defined as
If it had 21 sides (or more), you could also rotate it only 20 times. However, in such a case the definition of order of rotational symmetry would require you describe the figure as order 21 (or more). The definition is based on how many times you can rotate the figure, not how many times you choose to.
The number of positions a figure can be rotated to, without bringing inThus, if you look at sides (or vertices), and you can rotate your polygon 20 different ways and the sides (or vertices) are congruent with the original, it must have 20 sides.
any changes to the way it looks originally.
If it had 21 sides (or more), you could also rotate it only 20 times. However, in such a case the definition of order of rotational symmetry would require you describe the figure as order 21 (or more). The definition is based on how many times you can rotate the figure, not how many times you choose to.
