Question

\[\left(\begin{matrix}4 \\ 8\end{matrix}\right)\]

Answer 1

\binom{n}{k} or
\dbinom{n}{k}

Answer 2

{ n \choose k}
\[{ n \choose k}\]

Answer 3

\[\dbinom{n}{k}\]\[n \choose k\]\[\dbinom{n}{k}\]