in latex, when typesetting math, by default, parentheses (and other brackets) are always a constant height. So if you put something which is taller than one line in between parentheses, it will look strange, with the content sticking out past the parentheses at the top and/or bottom.

The fix for this (in latex) it to mark pairs of matching parentheses with the macros `\left` and `\right`, (for example: `\left( \frac{x}{y} \right)`) which informs latex that it should figure out how tall the content between the brackets is, and then resize the parentheses appropriately.