# Mathematical convention for writing products using dots

What would be the appropriate way of writing the following products involving numbers and variables (in LaTeX)?

• $2^{3}\cdot 5^{17}\cdot 11^{2}\cdot (x+y)$ $\qquad\text{or}\qquad$ $2^{3}\cdot 5^{17}\cdot 11^{2}(x+y)$

• $2^{3}\cdot 5^{17}\cdot 11^{2}\cdot x$ $\qquad\text{or}\qquad$ $2^{3}\cdot 5^{17}\cdot 11^{2}x$

Any other suggestions will be appreciated.

• Both seem OK, but for consistency, the ones on the left are better – Shailesh Sep 12 '16 at 2:29
• @Shailesh do you mean on the left? I'd say left for the same reason of consistency – Stahl Sep 12 '16 at 2:29
• @Stahl corrected ! – Shailesh Sep 12 '16 at 2:31
• I prefer the ones on the right, but both are acceptable. And $2^35^{17}11^2x$ etc. is better yet. – Brian M. Scott Sep 12 '16 at 6:28

The use of conjunction, that is writing $ab$ instead of $a\cdot b$, is common to denote multiplication. So, any notation you use is likely to be understood, and both are common: \begin{align} a\cdot b\cdot cx && \text{or} && a\cdot b\cdot c\cdot x \end{align} is fine. The same goes for \begin{align} a\cdot b\cdot c(x+y) && \text{or} && a\cdot b\cdot c\cdot (x+y). \end{align}
• I would not use any of these save under very unusual circumstances: $abcx$ and $abc(x+y)$ are far preferable in almost all cases. Obviously the dot (or parentheses) is needed in $2\cdot 3$, but it is wholly superfluous in $2a$ or $ab$; $2^k3^\ell$ is a borderline case, though even there I prefer the version without the dot. – Brian M. Scott Sep 12 '16 at 6:32