Radial distance (geometry)
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In geometry a radial distance, typically denoted r, is a coordinate in polar coordinate systems (r, θ). Basically the radial distance is the scalar Euclidean distance between a point and the origin of the system of coordinates.
Distance of two points in polar coordinates
The distance d between two points P1 and P2 with polar coordinates (r1, θ1) and (r2, θ2) is given by the polar distance formula:
This formula is derived from the law of cosines, applied to the triangle P1OP2 in which two sides have lengths r1 and r2 and the included angle is θ1 − θ2.