# The order of terms matters even when they commute

When writing an expression that consists of several terms, the conventions regarding their order appear arbitrary.

## Multiplication

It is usual to write:

• $$xy$$ and $$yx$$ in either order;
• $$5t$$ but not $$t5$$ (to avoid confusion with $$t_5$$ or $$t^5$$);
• $$x\sqrt{2}$$ but not $$\sqrt{2}x$$ (to avoid confusion with $$\sqrt{2x}$$). (See Something on the right of a radical)
• $$\sqrt{2}\sin x$$ but not $$\sin x \sqrt{2}$$ (to avoid confusion with $$\sin \left(x\sqrt{2}\right)$$).

$1 - x$
$-x + 1$