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By PiThagoras

Tags: Circle, Disk, Disc, Pi, Area, Surface Area

1

Posted: 2013-02-05
Area of a Disc
Area of a Disc
$$Area = \pi r^2$$

The area of a disc (the region inside a circle), often incorrectly called the area of a circle, is $\pi r^2$ when the circle has radius r. Here the symbol $\pi$ (Greek letter pi) denotes, as usual, the constant ratio of the circumference of a circle to its diameter. It is easy to deduce the area of a disk from basic principles: the area of a regular polygon is half its apothem times its perimeter, and a regular polygon becomes a circle as the number of sides increase, so the area of a disc is half its radius times its circumference (i.e. ${1 \over 2} r * 2 \pi r$ ).