Formulas obtained by finite algebraic operations such as addition, subtraction, multiplication, division, multiplication and square root of numbers and letters representing numbers or mathematical expressions containing letters are called algebraic expressions. All algorithms of numbers also apply to algebraic expressions. A single number or letter is also algebraic, and those with unequal symbols are not algebraic.

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In the range of real numbers, algebraic expressions can be divided into rational number expressions and irrational number expressions.

1, rational expression: rational expressions include algebraic expressions (rational expressions without letters in divisor) and fractions (rational expressions with letters in divisor and divisor not being 0). In this algebraic expression, only limited operations such as addition, subtraction, multiplication, division and integer power are performed on letters.

Algebraic expressions include monomials (products of numbers or letters or single numbers or letters) and polynomials (sums of several monomials).

2. Unreasonable formula: Algebraic formula containing the radical of letters or the non-integer power of letters is called irrational formula.

Number formula 1 operation, merging similar terms: merging similar terms in polynomials into one term is called merging similar terms. The rule of merging similar items is that the coefficients of similar items are added, and the results are taken as coefficients, and the indexes of letters remain unchanged.

2. Rules for removing brackets: put a "+"in front of brackets, remove brackets and the "+"in front of them, and the symbols in brackets remain unchanged; There is a "-"before the brackets. Remove the brackets and the "-"in front, and change the symbols of everything in brackets.

3. Rules for bracketing: After bracketing, put a "+"sign in front of the bracket, and all items in the bracket remain unchanged; After adding brackets, put a "-"in front of brackets, and all items in brackets should be changed.