 In the Euclidean plane, if p = ("p"1, "p"2) and q = ("q"1, "q"2) then the distance is given by

This is equivalent to the Pythagorean theorem.Alternatively, it follows from () that if the polar coordinates of the point p are ("r"1, θ1) and those of q are ("r"2, θ2), then the distance between the points is

In three-dimensional Euclidean space, the distance is

In general, for an "n"-dimensional space, the distance is

The square of the standard Euclidean distance, which is known as the squared Euclidean distance (SED), is also of interest; as an equation