Equation: How to generate "snaked"/curved/waved brackets/delimiters around an equation?

Question

I need to write this equation:

and I don't know how to do this line at the left and right.

Answer 1

There are some math fonts that provide those delimiters, I chose MnSymbol:

\documentclass{article}
\usepackage{amsmath}

\DeclareFontFamily{OMX}{MnSymbolE}{}
\DeclareFontShape{OMX}{MnSymbolE}{m}{n}{
    <-6>  MnSymbolE5
   <6-7>  MnSymbolE6
   <7-8>  MnSymbolE7
   <8-9>  MnSymbolE8
   <9-10> MnSymbolE9
  <10-12> MnSymbolE10
  <12->   MnSymbolE12}{}
\DeclareFontShape{OMX}{MnSymbolE}{b}{n}{
    <-6>  MnSymbolE-Bold5
   <6-7>  MnSymbolE-Bold6
   <7-8>  MnSymbolE-Bold7
   <8-9>  MnSymbolE-Bold8
   <9-10> MnSymbolE-Bold9
  <10-12> MnSymbolE-Bold10
  <12->   MnSymbolE-Bold12}{}

\DeclareSymbolFont{mnlargesymbols}{OMX}{MnSymbolE}{m}{n}
\SetSymbolFont{largesymbols}{bold}{OMX}{MnSymbolE}{b}{n}

\DeclareMathDelimiter{\lwavy}{\mathopen}{mnlargesymbols}{'136}{mnlargesymbols}{'136}
\DeclareMathDelimiter{\rwavy}{\mathclose}{mnlargesymbols}{'136}{mnlargesymbols}{'136}

\begin{document}

\begin{equation}
=\left\lwavy
\begin{aligned}
x  &= \frac{1}{\sqrt{1-\varphi^2}}
      \left(\frac{x-\mu}{\varphi}-\frac{\varphi(y-s_{1})}{\rho}\right)
\\
dx &= \kappa\sqrt{\varphi^2-\pi}\,dy
\end{aligned}
\right\rwavy
=
\end{equation}

\end{document}