Mathematical distance formula: distance between two places = speed × departure time. In mathematics, distance is one of the most basic concepts in functional analysis. The distance space defined by it connects topological space with normed linear space and other spaces, and it is the first contact concept of learning functional analysis.

Distance generally refers to the line segment between two points. In mathematics, distance is a scalar, has no direction and cannot be negative. At the same time, distance is one of the most basic concepts in functional analysis. Intuitively, if the sequence is regarded as a series of points on the real number axis, then the distance between any two points is equal to the absolute value of the difference between the two points.