The mathematical operation of subtracting a literal number from another literal number is called the subtraction of the literal numbers.
The literals in algebra involve in subtraction in some cases. So, one literal is needed to be subtracted from another literal number. It is very important for learners to understand the subtraction process and its result and also useful to study the algebra to the higher level.
There are two types of cases to perform the subtraction with literals in algebraic mathematics.
A literal number can be subtracted from another same literal but the subtraction of them is always zero because they both are equal in quantity and it does not depend on the value of the literal number.
$(1) \,\,\,\,\,$ $a-a$
For example, $a$ is a literal number and it is subtracted from the same literal number. The quantity that represented by the literal $a$ is subtracted by the same quantity. Hence, the subtraction of the literal $a$ from $a$ is equal to zero.
$\implies a-a = 0$
This rule is applicable to all same literals.
$(2) \,\,\,\,\,$ $b-b$
$\implies b-b = 0$
$(3) \,\,\,\,\,$ $c-c$
$\implies c-c = 0$
The literals represent unknown quantities. So, it is not possible to subtract a literal number from another literal number. Hence, the subtraction of two different literals is written as an algebraic expression.
$(1) \,\,\,\,\,$ $a-b$
$(2) \,\,\,\,\,$ $p-q$
$(3) \,\,\,\,\,$ $x-y$