How do I get a tilted equal sign for an equation?

Question

For example, this is what I am looking for:

Usually for limits where the value is 0 or 1 of a particular expression (e^x) in this case, you might see something like a tilted 45 degrees equal sign, and the value of that expression.

Not sure how to do it here.

Maybe something like a overbrace without the actual overbrace visible?

Answer 1

If you only want to draw one of those, this might be a bit of an overkill, but if you plan to do several annotations of that kind and wish to have access to more fancy features, this might be a reasonable way to go.

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{tikzmark}
\begin{document}
\[\lim_{x\to0}\tikzmarknode{ex}{\mathrm{e}^x}\left(2+4x\right)~=~2\]
\begin{tikzpicture}[overlay,remember picture]
\path[red] ([xshift=1pt,yshift=1pt]ex.north east) -- ++(45:{width("=")*1pt-1pt})
node[midway,sloped]{$=$} node[above right=-2pt]{$1$};
\end{tikzpicture}
\end{document}

Arguably somewhat clearer alternatives include

\documentclass{article}
\usepackage{mathtools}
\usepackage{tikz}
\usetikzlibrary{tikzmark}
\begin{document}
\[\lim_{x\to0}\tikzmarknode{ex}{\mathrm{e}^x}\left(2+4x\right)~=~2\]
\begin{tikzpicture}[overlay,remember picture]
\draw[red,->] ([xshift=1pt,yshift=1pt]ex.north east) --
++(45:{width("$\scriptstyle x\to0$")*1pt})
node[midway,sloped,above]{$\scriptstyle x\to0$} node[above right=-1pt]{$1$};
\end{tikzpicture}
\end{document}

which illustrates what I mean by "more fancy options".