The polar coordinates of the point P shown
to the right are written (r,θ) where r is the distance of
P from the origin and θ is the angle the line from the origin
to P makes with the x-axis, the angle being measured as θ
rotates counter-clockwise starting from the positive x-axis. At the
origin r=0, but θ is not well-defined, so we usually assign
to the origin the polar coordinates (0,θ) for any choice of
θ.
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