2. Mathematics is a science that studies the quantitative relations and spatial forms in nature. It composes the inner melody of nature with quantitative relations and spatial forms, reveals the essence of the world with concise and beautiful formulas and theorems, and regulates people's thinking order with rigorous language and logic. Mathematics is one of the basic disciplines of natural science, which originated from early human production activities. Early ancient Greece, ancient Babylon, ancient Egypt and ancient China all studied mathematics. Mathematics is a subject that studies concepts such as quantity, structure, change and spatial model. Through the application of abstraction and logical reasoning, the shape and motion of objects are counted, calculated, measured and observed. The basic elements of mathematics are: logic and intuition, analysis and reasoning, individuality and individuality. Mathematics can be divided into two categories, one is pure mathematics and the other is applied mathematics. Pure mathematics, also called basic mathematics, specializes in the internal laws of mathematics itself. The knowledge of algebra, geometry, calculus and probability introduced in primary and secondary school textbooks belongs to pure mathematics. A remarkable feature of pure mathematics is to temporarily put aside the specific content and study the quantitative relationship and spatial form of things in pure form. For example, it doesn't matter whether it is the area of trapezoidal rice fields or the area of trapezoidal mechanical parts. What everyone cares about is the quantitative relationship contained in this geometry. Applied mathematics focuses on explaining natural phenomena and solving practical problems, and is a bridge between pure mathematics and science and technology. It is often said that now is the information society, and the "information theory" which specializes in information is an important branch of applied mathematics.

3. Time is one of the seven dimensions in physics, and the symbol is T. In the International System of Units (SI), the basic unit of time is seconds, and the symbol is S.