Algebra is a branch of mathematics that uses letters or other symbols to represent unknown quantities, called variables. These variables and number values are combined to form equations. The rules of these equations follow the exact same rules as arithmetic, such as the commutative and associative laws for addition and multiplication. Functions are a special type of equation, where one variable can be uniquely defined in terms of the other. Another part of this topic is graphing of equations and functions using the Cartesian coordinate graph or polar coordinates. Also, covered in this topic is set theory or what constitutes a grouping of numbers.