In algebra, when letters, numbers, and arithmetic symbols occur together, the understanding is that the letters stand for variables, which are either symbols of their own, numbers not yet known, or numbers that change during the course of the problem (such as time). A polynomial is an algebraic expression in which the only arithmetic is addition, subtraction, multiplication and whole number exponentiation. If harder operations are used, such as division or square roots, then this algebraic expression is not a polynomial. Polynomials are often easier to use than other algebraic expressions.