1, π, Greek letter. In mathematics, pi is often mentioned. Pi, generally expressed by π, is a common mathematical constant in mathematics and physics.

It is defined as the ratio of the circumference to the diameter of a circle. It is also equal to the ratio of the area of a circle to the square of its radius. Accurate calculation of geometric shapes such as circle perimeter, circle area and sphere volume is the key value. On March 4th, 20 19, Google announced that pi has now reached 3 1.4 trillion digits after the decimal point.

I. Real numbers

1 is a general term for rational numbers and irrational numbers. Real and imaginary numbers * * * make up a complex number. Real numbers can be divided into rational and irrational numbers, or algebraic and transcendental numbers. Real number sets are usually represented by the black letter r, and real numbers are uncountable.

2. Real number is the core research object of real number theory. The set of all real numbers can be called real number system or real number continuum.

3. Any complete Archimedean ordered field can be called a real number system. It is unique in the sense of order-preserving isomorphism, and is often expressed by R. Because R is an arithmetic system that defines arithmetic operations, it is called the real number system.

4. Real numbers can be used to measure continuous quantities. Theoretically, any real number can be expressed as an infinite decimal, and to the right of the decimal point is an infinite series (cyclic or acyclic).

5. In practice, real numbers are often approximate to a finite decimal (n digits are reserved after the decimal point, and n is a positive integer). In the computer field, because computers can only store a limited number of decimal places, real numbers are often represented by floating-point numbers.

Second, the basic operation

1, the basic operations that can be realized by real numbers are addition, subtraction, multiplication, division, multiplication and so on. For non-negative numbers (that is, positive numbers and 0), you can also perform a root operation.

2. After adding, subtracting, multiplying, dividing and squaring real numbers, the result is still real numbers. Any real number can be raised to an odd power, and the result is still a real number. Only non-negative real numbers can be raised to even powers, and the result is still real numbers.