In mathematics, it refers to the difference between multiplication × and, for example, A B, 5×3. What if letters and numbers are mixed together? For example, 2a times 5, 2a times 2b.
No matter how it is expressed, the meaning is the same, which means multiplication. The general specification requirements are: the number is multiplied by X, and the letters are written together directly, such as AB; Formulas and formulas, if they are monomials and monomials, are generally multiplied by "",such as 2a 3ab, or polynomials and polynomials are written together directly, because there are brackets, such as (3a+2ab)(2a-3ab? )，-2ab(a+2b)