Fancy Chapter Styles in LaTeX

Question

How can I produce a fancy chapter like this one?

Answer 1

Here is a solution, using the  block style. Some parameter values may have to be adjusted if you use another basic font size or another font:

\documentclass[a4paper, 0pt,french]{book}%
\usepackage{geometry}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{babel}%
\usepackage{fourier, erewhon, cabin}
\usepackage{microtype}
\usepackage[pagestyles, clearempty, explicit]{titlesec}
\usepackage{eqparbox}
\usepackage{lipsum}%
\titleformat{\chapter}[block]{}{\eqmakebox[chap]{\Large\MakeUppercase{\sffamily\lsstyle\chaptername} %
\raisebox{-0.6\height}{\fontsize{50pt}{50pt}\selectfont\thechapter}\quad}}%
{0pt}{\huge\bfseries\raisebox{1ex}{\parbox[t]{\dimexpr\textwidth-\eqboxwidth{chap}\relax}{\titlerule[2pt]\vspace{1.25ex}#1}}}
\titlespacing*{\chapter}{0pt}{-32pt}{48pt}%

\begin{document}

\setcounter{chapter}{1}
\chapter{Problème parabolique\\ semi-linéaire dégénéré}

\lipsum[1-6]

\end{document} 

Answer 2

You can do it with titlesec, but I find it quite ugly.

\documentclass{book}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[french]{babel}

\usepackage{titlesec}
\usepackage{graphicx}

\titleformat{\chapter}[block]
 {\Large\bfseries}
 {\raisebox{-\height}{\sffamily\scriptsize\MakeUppercase{\chaptertitlename}}%
  \space\raisebox{-\height}{\bigchapternumber}\space}
 {0pt}
 {\printtitle}

\newlength\pretitlewidth
\newcommand\bigchapternumber{\resizebox{24pt}{!}{\mdseries\thechapter}}
\newcommand{\printtitle}[1]{%
  \settowidth{\pretitlewidth}{%
    {\sffamily\scriptsize\MakeUppercase{\chaptertitlename}}\space
    {\bigchapternumber}\space
  }%
  \parbox[t]{\dimexpr.8\textwidth-\pretitlewidth}{%
    \linespread{1.5}\selectfont
    \hrule depth 1pt
    \vspace{3ex}
    \raggedright\bfseries #1
  }%
}

\begin{document}

\setcounter{chapter}{1}

\chapter{Problème parabolique semi-linéaire dégénéré}

\end{document}