Big forward slash in math

It is also possible to put the equation into the brackets and then use the \middle/ instead of the regular slash.

So, for example, this equation:

\int \limits_{a}^{b} \frac{x}{y} / \int \limits_c^d \frac{x}{y}

would turn into this one:

\left[ \int \limits_{a}^{b} \frac{x}{y} \middle/ \int \limits_c^d \frac{x}{y} \right]

Or if you do not need any visible brackets, you may use the "fake" brackets instead:

\left. \int \limits_{a}^{b} \frac{x}{y} \middle/ \int \limits_c^d \frac{x}{y} \right.

For example:

\documentclass{article}

\begin{document}
\[
a=\textrm{\Huge VERYBIGSTUFF} \Biggm/ \textrm{\Huge VERYBIGSTUFF} 
\]

or (compare the spacing)

\[
a=\textrm{\Huge VERYBIGSTUFF} \Bigg/ \textrm{\Huge VERYBIGSTUFF} 
\]

In a real situation it would look nicer:

\Huge
\[
 a=\textrm{\Huge VERYBIGSTUFF} \Biggm/ \textrm{\Huge VERYBIGSTUFF} 
\]

or (compare the spacing)

\[
a=\textrm{\Huge VERYBIGSTUFF} \Bigg/ \textrm{\Huge VERYBIGSTUFF} 
\]

\end{document}

If you want a simple one-line solution, I always use just \left. - \right/ pair:

\begin{equation}
    a = \left.VERYBIGSTUFF \right/ VERYBIGSTUFF
\end{equation}

Example:

\begin{equation}
    a = \left.\int \limits_{a}^{b} \frac{x}{y} \right/ \int \limits_c^d \frac{x}{y}
\end{equation}

Output:

Very simple and efficient. Works well unless you have incredibly big stuff like in the answer of Steven B. Segletes