In algebra , a symbol (usually a letter) standing in for an unknown numerical value in an equation .
Commonly used variables include x and y (real-number unknowns), z (complex-number unknowns), t (time), r (radius), and s (arc length). Variables should be distinguished from coefficients, fixed values that multiply powers of variables in polynomial s and algebraic equation s. In the quadratic equation a x 2 + b x + c = 0, x is the variable and a , b and c are coefficients whose values must be specified to solve the equation. In translating word problems into algebraic equations, quantities to be determined can be represented by variables.
[c mediumvioletred] (as used in expressions)
eclipsing variable star