Affinely extended real number system

In mathematics, the affinely extended real number system is obtained from the real number system R by adding two elements: +∞ and −∞ (pronounced "positive  infinity" and "negative infinity"). These new elements are not real numbers. It is useful in describing various limiting behaviors in calculus and mathematical analysis, especially in the theory of measure and integration. The affinely extended real number system is denoted R or [−∞, +∞]. The affinely extended real number system should be distinguished from the  projectively extended real numbers by having two infinities, rather than one.
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