For 2D Math
In general, the best practice is to enter a multiplication symbol (*) for multiplication in any calculation. In some cases, you can instead insert a space character between two quantities to multiply them. This is called implicit multiplication.
For a product containing integers and decimals, implicit multiplication can be used only if the number occurs in the leftmost position in the product. For products of numbers, use explicit multiplication ($\mathbf{\cdot}$), entered by using the asterisk (*) symbol on your keyboard. However, you can use implicit multiplication for products containing fractions.
Example 1
Valid

$2x$ = ${2}{}{x}$

Not valid

$23$
${}$
To fix the error, insert a multiplication symbol between the two quantities instead of a space.

Valid

$2\cdot 3$ = ${6}$
${}$



Example 2
Not valid

$2.5$
$2.35.3333333333$
To fix the error, insert a multiplication symbol between the two quantities instead of a space.

Valid

$2\cdot .5$ = ${1.0}$${}$
$2.3\cdot 5.3333333333$ = ${12.26666667}$${}$

Valid

$\frac{2}{3}\frac{5}{3}$ = $\frac{{10}}{{9}}$



All of the errors shown in these examples are due to the rule that a number cannot appear as the righthand operand of an implicit multiplication operation. In such cases, use of explicit multiplication (*) can avoid the error. For more information, see 2DMathDetails.
Tip: Troubleshooting your mathematics is easier if you use explicit multiplication symbols.