Editing Equation (section)

===Parameters and unknowns===
{{see also|Expression (mathematics)}}
Equations often contain terms other than the unknowns. These other terms, which are assumed to be ''known'', are usually called ''constants'', ''coefficients'' or ''parameters''.

An example of an equation involving ''x'' and ''y'' as unknowns and the parameter ''R'' is

:<math> x^2 +y^2 = R^2 .</math>

When ''R ''is chosen to have the value of 2 (''R ''= 2), this equation would be recognized in [[Cartesian coordinates]] as the equation for the circle of radius of 2 around the origin. Hence, the equation with ''R'' unspecified is the general equation for the circle.

Usually, the unknowns are denoted by letters at the end of the alphabet, ''x'', ''y'', ''z'', ''w'', ..., while coefficients (parameters) are denoted by letters at the beginning, ''a'', ''b'', ''c'', ''d'', ... . For example, the general [[quadratic equation]] is usually written ''ax''<sup>2</sup>&nbsp;+&nbsp;''bx''&nbsp;+&nbsp;''c''&nbsp;=&nbsp;0.

The process of finding the solutions, or, in case of parameters, expressing the unknowns in terms of the parameters, is called [[Equation solving|solving the equation]]. Such expressions of the solutions in terms of the parameters are also called ''solutions''.

A [[system of equations]] is a set of ''simultaneous equations'', usually in several unknowns for which the common solutions are sought. Thus, a ''solution to the system'' is a set of values for each of the unknowns, which together form a solution to each equation in the system. For example, the system
:<math>\begin{align}
3x+5y&=2\\
5x+8y&=3
\end{align}
</math>
has the unique solution ''x''&nbsp;=&nbsp;−1, ''y''&nbsp;=&nbsp;1.