Literal expression কী?

A literal expression is a computation containing one or more letters, each standing for a number. Writing conventions:

• the sign $\times$ is dropped before a letter or a bracket: $3 \times a = 3a$, $a \times b = ab$, $2 \times (x + 5) = 2(x + 5)$;
• but it stays between two numbers: $3 \times 5$ cannot be written $35$!
• $a \times a$ is written $a^2$ (“$a$ squared”), $a \times a \times a = a^3$;
• $1a$ is written $a$, and $0a$ is $0$.