In [[mathematics]], when a letter is used to represent a number or set of numbers it is called an '''unknown'''. This letter usually has a very specific range of values, unlike a [[variable]] which can be changed arbitrarily to alter the value of a [[function]] which acts on the variable. | In [[mathematics]], when a letter is used to represent a number or set of numbers it is called an '''unknown'''. This letter usually has a very specific range of values, unlike a [[variable]] which can be changed arbitrarily to alter the value of a [[function]] which acts on the variable. |