Editing Analytic geometry (section)

===Polar coordinates (in a plane)===
{{main|Polar coordinate system}}
In [[polar coordinates]], every point of the plane is represented by its distance ''r'' from the origin and its [[angle]] ''θ'', with ''θ'' normally measured counterclockwise from the positive ''x''-axis. Using this notation, points are typically written as an ordered pair (''r'', ''θ'').  One may transform back and forth between two-dimensional Cartesian and polar coordinates by using these formulae: <math display="block">x = r\, \cos\theta,\, y = r\, \sin\theta; \, r = \sqrt{x^2+y^2},\, \theta = \arctan(y/x).</math> This system may be generalized to three-dimensional space through the use of [[Cylindrical coordinates|cylindrical]] or [[Spherical coordinates|spherical]] coordinates.