The polar coordinate system consists of a pole and a polar axis.
The pole is a fixed point, and the polar axis is a directed ray whose endpoint
is the pole. Every point in the plane of the polar axis can be specified
according to two coordinates: *r*, the distance between the point and the pole,
and *θ*, the angle between the polar axis and the ray containing the point
whose endpoint is also the pole.

Figure %: The polar coordinate system

To convert equations between polar coordinates and rectangular coordinates, consider the following diagram:

Figure %: The *x* and *y* coordinates in the polar coordinate system

To convert from rectangular to polar coordinates, use the following equations:
*x* = *r* cos(*θ*), *y* = *r* sin(*θ*). To convert from polar to rectangular
coordinates, use these equations: *r* = *sqrtx*^{2}+*y*^{2}, *θ* = arctan().

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