Natural number 1, 2, 3, 4, etc. Everything that represents the number of objects is called a natural number.

Prime number and composite number An integer greater than 1 is called a prime number if it cannot be divisible by other positive integers except itself and 1. A number greater than 1 is a composite number if it can be divisible by other positive integers except itself and 1. 1 is neither a prime number nor a composite number.

There are only two real numbers with different signs, one of which is called the opposite of the other. The antonym of zero is zero.

Absolute value The absolute value of a positive number is itself, the absolute value of a negative number is its reciprocal, and the absolute value of zero is zero.

From the number axis, the absolute value of a real number is the distance between the point representing this number and the origin.

The quotient of the reciprocal of 1 divided by a nonzero real number is called the reciprocal of this real number. Zero has no reciprocal.

Complete Square Number If the square of rational number A is equal to rational number B, then this rational number B is called complete square number.

Square Root If a number whose power is n (n is an integer greater than 1) is equal to A, this number is called the power square root of A..

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

Arithmetic root The positive n-th square root of a positive number is called the n-th square root of a, the arithmetic root of zero is zero, and the negative number has no arithmetic root.

Algebraic expression is an expression obtained by connecting numbers or letters representing numbers with a finite number of operation symbols (addition, subtraction, multiplication, division, multiplication and root).

Algebraic value replaces the letters in the algebraic expression with a numerical value, and the result calculated when the letters take this numerical value is called algebraic value.

Classification of algebraic expressions

Algebraic expressions that only contain addition, subtraction, multiplication, division and multiplication are called rational expressions.

Algebraic expressions with letters under the root sign of irrational numbers are called irrational number expressions.

Algebraic formulas without division or rational formulas with division but without letters are called algebraic formulas.

The rational letters are called fractions in fractional division.

Okay？