Editing Equation (section)

===Parametric equations===
{{main|Parametric equation}}
A [[parametric equation]] for a [[curve]] expresses the [[coordinates]] of the points of the curve as functions of a [[variable (mathematics)|variable]], called a [[parameter]].<ref>Thomas, George B., and Finney, Ross L., ''Calculus and Analytic Geometry'', Addison Wesley Publishing Co., fifth edition, 1979, p. 91.</ref><ref>Weisstein, Eric W. "Parametric Equations." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/ParametricEquations.html</ref> For example,
:<math>\begin{align}
x&=\cos t\\
y&=\sin t
\end{align}</math>
are parametric equations for the [[unit circle]], where ''t'' is the parameter. Together, these equations are called a parametric representation of the curve.

The notion of ''parametric equation'' has been generalized to [[Surface (topology)|surfaces]], [[manifold]]s and [[algebraic variety|algebraic varieties]] of higher [[dimension of a manifold|dimension]], with the number of parameters being equal to the dimension of the manifold or variety, and the number of equations being equal to the dimension of the space in which the manifold or variety is considered (for curves the dimension is ''one'' and ''one'' parameter is used, for surfaces dimension ''two'' and ''two'' parameters, etc.).