Editing Subtangent (section)

==Polar definitions==
[[Image:PolarSubtangentDiagram.svg|thumb|250px|right|Polar subtangent and related concepts for a curve ('''black''') at a given point ''P''. The tangent and normal lines are shown in <span style="color:green;">green</span> and <span style="color:blue;">blue</span> respectively. The distances shown are the <span style="color:#800000;">'''radius'''</span> (''OP''), <span style="color:#808000;">'''polar subtangent'''</span> (''OT''), and <span style="color:#800080;">'''polar subnormal'''</span> (''ON''). The angle θ is the radial angle and the angle ψ of inclination of the tangent to the radius or the polar tangential angle.]]
Let ''P''&nbsp;=&nbsp;(''r'',&nbsp;θ) be a point on a given curve defined by [[polar coordinates]] and let ''O'' denote the origin. Draw a line through ''O'' which is perpendicular to ''OP'' and let ''T'' now be the point where this line intersects the tangent to the curve at ''P''. Similarly, let ''N'' now be the point where the normal to the curve intersects the line. Then ''OT'' and ''ON'' are, respectively, called the '''polar subtangent''' and '''polar subnormal''' of the curve at ''P''.