**When two or more terms are joined together with the help of mathematical operators namely addition and subtraction are called expressions.**

Most of the times we come across the expressions with constant values like 5 + 4 makes 9. This can be said as “Five added to 4 makes nine” . These expressions can sometimes contain variables too, whose values are not known.

**The unknown terms are called variables, and the value of the same variable may vary from place to place.**

Let us consider a variable say “x”. The value of ‘x’ may be 5 in one expression and may be 40 in another expression. So the value of the variable is changing, depending upon the expression it stores it. The expression, which is made by the combination of the variables and the constants are called as variable expression in math.

Let us take a statement say: “two times of ‘x’ is added to 6“.

Here we could say that ‘x’ is a variable which may contain different values and 6 is a constant value which remains unchanged. Now if we write two times x, it means 2*x. Now further we observe that is says two times of ‘x’ is added to 6, which says that we will add 6 to the number which is twice of ‘x’. Thus this expression will be written as 2x + 6.

In the same we observe that the expression can be used to find the values of the variables when they are equated in form of the equation.