2x/3 is a monomial. 0.4X+3 is a polynomial. X/y is not an algebraic expression, but a fraction. It is also part of the fractional form. A rational expression in algebraic expression. If there is no division or fraction, if there is a division and fraction, but there is no variable in the division or denominator, it is called an algebraic expression. If the algebraic letters are divisible, then the formula is called fractional decimal. ) monomials and polynomials are collectively called algebraic expressions. Algebraic expression: an expression obtained by finite algebraic operations such as addition, subtraction, multiplication, division, multiplication and square root of numbers and letters representing numbers, or a mathematical expression containing letters is called algebraic expression. For example: ax+2b, -2/3, b 2/26, √a+√2, etc. Note: 1, excluding equal sign (=, ≦), unequal sign (≦, ≤, ≥,