Sometimes, you might have to use parentheses within parentheses. According to the APA style, in this case, you will need to create these two levels of enclosure by using brackets inside of parentheses.

• For example: (We have also looked at the study that found the amount of time teenagers spend on their phones each week [N. Iqbal, 2018], but these results are not mentioned here).

With mathematical equations, however, it works the other way around: for two levels of enclosure, parentheses go inside brackets. For three levels, curly brackets can be added outside.

• For example: The students were asked to solve the following equation: 7[2x+1(x+5)]=1470.