Expressions using Letter-Numbers - Omission of the Multiplication Symbol in Algebra

In Algebra, letters (literals) are used to represent numbers. When multiplying a number and a literal, or two literals, the multiplication sign $\times$ is usually omitted to keep expressions concise.

When a constant (number) and a variable (letter) are multiplied, the number is written first, followed by the letter. For example, $3 \times y$ is written as $3y$. Here, $3$ is called the numerical coefficient of $y$.

When two or more literals are multiplied together, they are written side-by-side without any symbol. For example, $a \times b$ is written as $ab$. By convention, we write them in alphabetical order ($abc$ instead of $cba$).

The product of a literal with itself is expressed using exponents or powers. For example, $x \times x$ is written as $x^2$ and $y \times y \times y$ is written as $y^3$.

The multiplication of any literal by $1$ results in the literal itself, and the $1$ is typically omitted. Thus, $1 \times x$ is written simply as $x$. Similarly, $-1 \times x$ is written as $-x$.

If an expression involves brackets, the multiplication sign between the term outside and the bracket is also omitted. For example, $2 \times (a + b)$ is written as $2(a + b)$.