Extended real number line

via Extended real number line – Wikipedia, the free encyclopedia.

In mathematics, the **affinely extended real number system** is obtained from the real number system **R** by adding two elements: +∞ and −∞ (read as **positive infinity** and **negative infinity** respectively). The **projective extended real number system** adds a single object, ∞ (infinity) and makes no distinction between “positive” or “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 [−∞, +∞].

When the meaning is clear from context, the symbol +∞ is often written simply as ∞.

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