It can be any letter of any alphabet: Roman, Greek.
An unknown variable
An algebraic expression uses a letter to represent an unknown quantity.
If you are talking about math then its usually " x " but if that is already use in the expression and you want to use another symbol to represent a DIFFERENT number then you can use y or a or so on.
Not a letter or number .It is Special Character
dendrites
An unknown variable
Variable
In statistics, letter such as; a,..x..,z, is a variable used to represent an unknown value.
An Algebraic expression is any expression (equation) that contains a letter where a number should be.
An algebraic expression uses a letter to represent an unknown quantity.
a variable
It is an element, so you represent it with the letter F
An algebraic expression will normally include one or more variables that is represented by a letter or some non-numeric symbol.
a variable.
The algebraic expression is p/89
the def for variable is a letter or symbol used to represent a missing number in an algebrac expression
In a mathematial equation the letters wither represent a variable or a constant.