A mathematical statement that indicates equality with the use of an equal sign (=) between two expressions. In programming languages, assignment statements are written in equation form. See also assignment statement.
In mathematics, expression that represents the equality of two expressions involving constants and/or variables, and thus usually includes an equals sign (=). For example, the equation A = pr2 equates the area A of a circle of radius r to the product pr2.
The algebraic equation y = mx + c is the general one in coordinate geometry for a straight line.
If a mathematical equation is true for all variables in a given domain, it is sometimes called an identity and denoted by º.
Thus (x + y)2 º x2 + 2xy + y2 for all x, y Î R.
An indeterminate equation is an equation for which there is an infinite set of solutions—for example, 2x = y. A diophantine equation is an indeterminate equation in which the solution and terms must be whole numbers (after Diophantus of Alexandria, c. AD 250).

ETYM Pref. bi- + quadrate.
An algebraic equation of the fourth degree; SYN. biquadratic, quartic, fourth power.

A polynomial of the fourth degree; SYN. biquadratic polynomial, quartic polynomial.
Number's fourth power; equation involving fourth power of unknown quantity.