Reduce margins (left and right)

Question

This is my code:

\documentclass[a4paper, french, 12pt]{article}
\usepackage{amsfonts}
\usepackage{indentfirst}
\usepackage{xcolor}
\usepackage{array}
\usepackage{booktabs}
\oddsidemargin 0in
\topmargin 0in
\evensidemargin 0in
\topskip 0in

\title{\textsc{\fbox{Rappel de trigonométrie}}}
\date{}
\begin{document}

    \maketitle
    \pagenumbering{gobble}

    \section{\textit{\color{red}Valeurs remarquables et formules élémentaires}}

Voici un tableau des valeurs remarquables concernant les fonctions trigonométriques: 

\begin{center}
\[
\begin{array}{@{} l *{6}{>{\displaystyle}c} @{}}
\toprule
x       & 0 &\frac{\pi}{6}   &\frac{\pi}{4}   &\frac{\pi}{3}   &\frac{\pi}{2}&\pi\\ 
\midrule
\cos(x) & 1 &\frac{\sqrt3}{2}&\frac{\sqrt2}{2}&\frac{1}{2}     &0            &-1 \\ 
\addlinespace
\sin(x) & 0 &\frac{1}{2}     &\frac{\sqrt2}{2}&\frac{\sqrt3}{2}&1            &0  \\ 
\addlinespace
\tan(x) & 0 &\frac{1}{\sqrt3}&1               &\sqrt3          &\infty       &0  \\ 
\bottomrule
\end{array}
\]
\end{center}
\par
Les fonctions $\cos$ et $\sin$ sont reliées par la formule suivante:
\begin{center}
\fbox{$\forall x \in \mathbb{R}, \cos(x) + \sin(x) = 1$}
\end{center}

\end{document}

Answer 1

This is a summary of the discussion in the comments, which I will be happy to delete. Note also that there is the \boxed command (provided by the amsmath package) for boxed displayed equations.

Observe that I've omitted both center wrappers.

Note that there should be no blank lines between text and a displayed equation.

\documentclass[a4paper, french, 12pt]{article}
\usepackage{amssymb,amsmath} % 'amssymb' loads 'amsfonts' automatically
%\usepackage{indentfirst} %not needed if 'babel' is loaded with option 'french'
\usepackage{babel}
\usepackage[T1]{fontenc}

\usepackage{xcolor,array,booktabs}
\usepackage[left=0.5in,right=0.5in]{geometry}

\usepackage{titlesec}
\titleformat{\section}
{\normalfont\bfseries\itshape\color{red}}
{\Roman{section})}
{1em}
{}

\title{\fbox{\Huge\textsc{Rappel de Trigonométrie}}}
\date{}
\begin{document}
\maketitle

\pagenumbering{gobble}

\section{Valeurs remarquables et formules élémentaires}

Voici un tableau des valeurs remarquables concernant les fonctions trigonométriques: 
\[
\begin{array}{@{} l *{6}{>{\displaystyle}c} @{}}
\toprule
x       & 0 &\frac{\pi}{6}   &\frac{\pi}{4}   &\frac{\pi}{3}   &\frac{\pi}{2}&\pi\\ 
\midrule
\cos(x) & 1 &\frac{\sqrt3}{2}&\frac{\sqrt2}{2}&\frac{1}{2}     &0            &-1 \\ 
\addlinespace
\sin(x) & 0 &\frac{1}{2}     &\frac{\sqrt2}{2}&\frac{\sqrt3}{2}&1            &0  \\ 
\addlinespace
\tan(x) & 0 &\frac{1}{\sqrt3}&1               &\sqrt3          &\infty       &0  \\ 
\bottomrule
\end{array}
\]

Les fonctions $\cos$ et $\sin$ sont reliées par la formule suivante:
\[
\boxed{\forall x \in \mathbb{R},\ \cos^2(x) + \sin^2(x) = 1}
\]

\end{document}