Strikeout Equations or Paragraphs – Is It Possible?

Question

I have a document in which I want to strikeout whole paragraphs including all equation and eqnarray environments. Available options such as sout (from ulem) works on paragraph but not in equations. Also cancel (from cancel) work only inside math, but not in paragraphs and in eqnarrays only one line at a time.

Is there a package or command that will allow to strikeout with, for example:

\strike{
%long paragraph or equation or eqnarray
}

Preferably I need a diagonal strikeout but any alternative would work.
Here it is an example:

\documentclass[]{revtex4}
  \usepackage{amsmath,amsfonts,amsthm,amssymb}
  \usepackage{cancel}

  \begin{document}
  par

  \begin{eqnarray}
  %\cancel{ %cancel doesn't work for eqnarray
  f(x) & = & \sin(x) \\
  g(x) & = & \cos(x)
  %}
  \end{equation}

  par

  \end{document}

Answer 1

cancel works with aligned environment, but in this case the equation numbers are lost.

\documentclass[]{revtex4}
  \usepackage{amsmath,amsfonts,amsthm,amssymb}
  \usepackage{cancel}
%  \usepackage{ulem}

  \begin{document}

    \[%
    \cancel{%
      \begin{aligned}
        f(x) &=  \sin(x) \\
        g(x) &=  \cos(x)
      \end{aligned}
    }%
    \]


  \end{document}