# Variable

Is a symbol for a number we don’t know yet. X is the variable in the term 4X.

The “letters” in an equation are the variables.

The **variable** nature of **letters'** sizes makes them very difficult to manage.

**Example 1**

`a^2+9^2=100`

In the above equation “a” is the variable.

**Example 2**

`a^2+b^2=c^2`

In the above equation a, b and c are all variables.

**Example 3**

`136=\pir^2`

In the above equation r is the variable.