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cylindrical coordinates[sə′lin·drə·kəl ‚kō′ȯrd·ən·əts]
The cylindrical coordinates of a point M are the three numbers r, θ, and z characterizing the position of M in space (see Figure 1). The coordinates are called cylindrical because the coordinate surface r = const is a cylinder
whose elements are parallel to the z-axis. The relation between the cylindrical coordinates and the rectangular coordinates x, y, and z of M is given by the equations x = r cos θ, y = r sin θ, and z = z.