This quick project gives a visual demonstration of what equilateral polygons with a chosen number of sides look like. Use either the slider or the left/right arrow keys to change the number of sides. Note that the more sides the polygon has, the closer to a circle it appears to be. A perfect circle is theoretically what you get with an infinite number of sides, but in practice anything above about 25 already appears to be a circle.
This project works particularly well in Turbo mode. Shift-click the green flag to enable turbo mode. Shift-click it again to switch off Turbo mode.