\overbrace, \underbrace
\overbrace{a} + \underbrace{a+b+c+d+E} + \overbrace{\sqrt{b+c+15.4} - \cos 2.3\pi \times 41}
\left \{ \overbrace{\underbrace{\frac{2x+3}{\log_{10} 2x^2}}} \right \} = \underbrace{\overbrace{ \left \{ \frac{2x+3}{\log_{10} 2x^2} \right \} } }More information on these commands may be found in Sec. 5.9 of the WebTeX documentation.
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