Rational Numbers: Rational Numbers are divided into positive rational numbers, negative rational numbers and 0. Rational numbers can be converted into decimals, where integers can be regarded as decimals followed by zeros, and any decimals with infinite cycles are called rational numbers. Such as: 3.121212121212. ...

Irrational number: infinite cyclic decimal. Irrational numbers must meet three conditions: ① it is a decimal; ② is an infinite decimal; ③ No cycle. Pi π = 3. 14 1592653 ...

Complex number: a+bi number. Where a and b are real numbers, and I is a number satisfying I2 =- 1. Because the square of any real number is not equal to-1, I is not a real number, but a new number other than a real number. In the complex number A+Bi, A is called the real part of the complex number, B is called the imaginary part of the complex number, and I is called the imaginary part. When the imaginary part is equal to zero, this complex number is a real number; When the imaginary part is not equal to zero, this complex number is called imaginary number, and if the real part of imaginary number is equal to zero, it is called pure imaginary number. As can be seen from the above, complex set contains real set, so it is an extension of real set.

Real numbers: Rational numbers and irrational numbers are collectively called real numbers.

Integer: Integers include positive integers, negative integers and 0.

Such as positive integer: 1, 2, 3. ...

Negative integers:-1, -2, -3 ...

Natural number: natural number is the number generated when people count (such as "there are three apples"), so the number used to represent the number of objects is called natural number. There is no object, of course it can be represented by "0", so "0" is also a natural number.

The meaning of imaginary number

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(1) [unreliable number]: imaginary number (2) [imaginary number]: A+Bi and B in a complex number are not equal to zero, which is called imaginary number (3) [temporarily unavailable in English]: Chinese words that do not represent specific numbers are in mathematics. If the square of a number is negative, then the number is imaginary. All imaginary numbers and real numbers make up a complex number. This number has a special symbol "I" (imaginary number). We can write the positive imaginary number as (+i), the negative imaginary number as (-i), regard+1 as a positive real number and (-1) as a negative real number. So we can say √ ~ (-1) = i. We can even draw the imaginary system when drawing. If the positive real number system is represented by a straight line with zero as the midpoint, then one side of zero is positive real number and the other side is negative real number. In this way, when you make a straight line that intersects the straight line at right angles through the zero point, you can represent the imaginary system along the second straight line. On the second straight line, the number on one side of 0 point is a positive imaginary number, and the number on the other side of 0 point is a negative imaginary number. The word "imaginary number" was invented by Descartes, a famous mathematician in17th century, because the concept at that time thought it was a nonexistent real number. Later, it was found that the imaginary number can correspond to the vertical axis on the plane, which is as real as the real number corresponding to the horizontal axis on the plane. The plane composed of imaginary axis and real axis is called complex plane, and each point on the complex plane corresponds to a complex number. Note: imaginary numbers also have sizes; Imaginary numbers are not one-dimensional positive and negative, but two-dimensional positive and negative; Integers should be accurately divided into real integers and imaginary integers.