The parentheses in the formula Al(OH)3 are used to indicate that there are three hydroxide (OH) groups associated with each aluminum (Al) atom in the compound. This information is important for understanding the chemical structure and properties of the compound.

Without the parentheses, the formula would simply be written as AlOH3, which could be interpreted as representing a compound with one aluminum atom and three hydroxide groups. However, this would be incorrect, as the actual compound contains one aluminum atom and three hydroxide groups that are bonded to it in a specific way.

By using parentheses, we can clearly indicate that the three hydroxide groups are all bonded to the aluminum atom, and that they are not simply separate molecules or ions in the compound. This allows us to accurately represent the chemical structure of the compound and understand its properties.