What is Algebraic Expression

Unlike number expressions, algebraic expressions can contain variables.

Following is example of algebraic expression:

$$${\color{green}{{{x}}}}{\color{blue}{{\times}}}{\color{red}{{{2}}}}{\color{blue}{{+}}}{\color{red}{{{3}}}}{\color{blue}{{-}}}{\color{green}{{{x}}}}{\color{blue}{{\times}}}{\color{green}{{{y}}}}{\color{blue}{{+}}}{{\color{green}{{{x}}}}}^{{\color{red}{{{2}}}}}{\color{blue}{{+}}}{{\left({\color{red}{{{5}}}}{\color{blue}{{-}}}{\color{green}{{{x}}}}\right)}}^{{{\color{green}{{{y}}}}}}$$$

Constants are red, variables are green, operations are blue.

Sometimes, we can discard multiplication and write $$${x}{y}$$$ instead of $$${x}\times{y}$$$. This is possible to do, if you really sure that others will not have to guess, what you wrote.

For example, you can write $$${2}{x}$$$ instead of $$${2}\cdot{x}$$$.

However, you can't write $$${123}$$$ instead of $$${12}\times{3}$$$, because you mean $$${12}\times{3}={36}$$$, but others see $$$123$$$.