Expressions using Letter-Numbers - The Notion of Letter-Numbers

A 'Letter-Number' or a Literal is a letter of the alphabet used to represent a number whose value is not yet known. Usually, lowercase letters like $x, y, z, a, b, c$ are used.

A Constant is a symbol that has a fixed numerical value, such as $5, -10, \frac{1}{2}$, or $0$.

A Variable is a symbol (usually a literal) that can be assigned different numerical values depending on the context.

Operations on Literals: Literals follow the same rules of addition, subtraction, multiplication, and division as regular numbers.

Addition: The sum of $x$ and $y$ is written as $x + y$.

Subtraction: $y$ subtracted from $x$ is written as $x - y$.

Multiplication: $x$ multiplied by $y$ is written as $xy$ or $x \cdot y$. Note that $3 \times x$ is written as $3x$.

Division: $x$ divided by $y$ is written as $\frac{x}{y}$ (where $y \neq 0$).

Power of a Literal: If a literal is multiplied by itself multiple times, it is written in exponential form. For example, $x \times x = x^2$ and $y \times y \times y = y^3$.