$\displaystyle z=(4+\sqrt15)^1/3$
Do either:
[tex]\left\{ \frac{1}{2} \right\}[/tex], which gives us $\displaystyle \left\{ \frac{1}{2} \right\}$
OR
[tex]\{ \frac{1}{2} \}[/tex], which gives us $\displaystyle \{ \frac{1}{2} \}$
Note the difference between these. The first one looks better...the second one seems odd....
--Chris
Better still (in my opinion), do
[tex]\left\{ \tfrac{1}{2} \right\}[/tex], which gives us $\displaystyle \left\{ \tfrac{1}{2} \right\}$
The textstyle fractions usually (not always) look better than displaystyle when dealing with single-digit numbers in the fraction.
... or you can use \pmod, as in [tex]x \equiv 6 \pmod{9}[/tex], to get $\displaystyle x \equiv 6 \pmod{9}$.
Personally, I think that \pmod leaves too much space before the first parenthesis, so I put in a couple of small backspaces (\!\!), to get $\displaystyle x \equiv 6\!\! \pmod{9}$.