Infinity is equivalent to a specific number in high school mathematics. For example, numbers like 1 9 10000 are only expressed as infinity, and r is the set of rational numbers including 1 2 3 4 and all irrational numbers. Infinity is one of the elements. In other words, R is an integer axis, and infinity is just a point on the number axis, which is the difference, so we can't express R with infinity.