Long expressions can extend beyond their containers: \(\displaystyle\sum_{n=1}^{10} {1\over n} = {1\over 1} + {1\over 2} + {1\over 3} + {1\over 4} + {1\over 5} + {1\over 6} + {1\over 7} + {1\over 8} + {1\over 9} + {1\over 10}\) You could turn on line-breaking to solve the problem, but may prefer not to. Instead, you can rescale the math after it has been typeset.