Editing Analytic geometry (section)

==Geometric axis==

Axis in geometry is the perpendicular line to any line, object or a surface.

Also for this may be used the common language use as a: normal (perpendicular) line, otherwise in engineering as ''axial line''.

In [[geometry]], a '''normal''' is an object such as a line or vector that is [[perpendicular]] to a given object. For example, in the two-dimensional case, the '''normal line''' to a curve at a given point is the line perpendicular to the [[tangent line]] to the curve at the point.

In the three-dimensional case a '''surface normal''', or simply '''normal''', to a [[Surface (mathematics)|surface]] at a point ''P'' is a [[vector (geometry)|vector]] that is [[perpendicular]] to the [[Tangent space|tangent plane]] to that surface at ''P''. The word "normal" is also used as an adjective: a [[line (geometry)|line]] normal to a [[plane (geometry)|plane]], the normal component of a [[force]], the '''normal vector''', etc. The concept of '''normality''' generalizes to [[orthogonality]].