Definition: Any finite decimal or infinite cyclic decimal is a rational number. The decimal of infinite cycle is called irrational number.

(Rational numbers can always be expressed by finite decimals or infinite cyclic decimals)

Generally speaking, if the square of a positive number x is equal to a, then this positive number x is called the arithmetic square root of a.

In particular, we stipulate that the arithmetic square root of 0 is 0.

Generally speaking, if the square of a number X is equal to A, then this number X is called the square root of A (also called square root).

Positive numbers have two square roots; 0 has only one square root, which is 0 itself; Negative numbers have no square root.

The operation of finding the square root of a number is called square root, where a is called square root.

Generally speaking, if the cube of a number X is equal to A, then this number X is called the cube root of A (also called cube root).

The cube root of a positive number is a positive number; The cube root of 0 is 0; The cube root of a negative number is a negative number.

The operation of finding the cube root of a number is called square root, where a is called square root.

Rational numbers and irrational numbers are collectively called real numbers, that is, real numbers can be divided into rational numbers and irrational numbers.

Every real number can be represented by a point on the number axis; On the contrary, every point on the number axis represents a real number. That is, there is a one-to-one correspondence between real numbers and points on the number axis.

On the number axis, the point on the right represents a larger number than the point on the left.