Approximate equality is a concept used primarily in physics and engineering, and also occasionally in mathematics. Two quantities are approximately equal when they are close enough in value so the difference is inconsequential in practical terms. Approximate equality is symbolized by a squiggly equal sign ( ). As an example of how approximate equality can be used in mathematics, consider the positive square root of 2 (or 2 1/2 ). This is an irrational number ; when written in decimal form, it is nonterminating and nonrepeating.