Approximation for pi

Pi is defined as the circle's circumference divided by the diameter. . Archimedes used inscribed and circumscribed polygons to find an approximation for pi. In the demonstration below, u and v represent approximations for pi by dividing the perimeter of the polygon by the diameter of the circle. Use the slider to see what happens as the number of sides increase for the inscribed and circumscribed polygon. How many sides are needed to determine the first 3 digits of pi? How do you know this?