Math expects that for every opening bracket there will be a closing one. If you forget a bracket, Math places an inverted question mark in place of the missing bracket. The inverted question mark disappears when the opening bracket has a matching closing bracket. This behavior is appropriate the majority of time, when matching brackets make sense mathematically. However, an unpaired bracket is sometimes necessary. In such cases, the solution depends on whether you are using regular non-scalable brackets or scalable brackets.