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While writing this paragraph I wanted to align the \leqtogether but I don't know how, here's the code I worked with :

    \textbf{Théoriquement :}\\
On sait que l'expression mathématique d'une tension s'écrit sous la forme suivante :
$$u(t)=U_m \cos(2\pi f t)$$
Pour que le signal modulant aura une expression mathématique, on pose $U_m=A\left(m\cos(2\pi f_s t)+1\right)$ 
\begin{align*}
-1&\leq \cos(2\pi f_s t)\ \ \ \ \ \ \leq 1\\
-m&\leq m\cos(2\pi f_s t)\ \ \  \leq m\\
1-m&\leq m\cos(2\pi f_st)+1\ \  \leq 1+m\\
A(1-m)&\leq A\left(m\cos(2\pi f_s t)+1\right)\leq A(1+m)
\end{align*}

Any helpful idea ?

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  • The alignat* environment should work. – leandriis Feb 19 at 18:39
  • @leandriis Oh thanks, I didn't know that this environment exists, Thank you :D – Eduardo.ni Feb 19 at 18:41
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I propose these improvements with align* and eqparbox, so that the middle term is centred between the \leq signs:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[french]{babel} 
\usepackage{amsmath}
\usepackage{eqparbox}
\newcommand\eqmathbox[2][M]{\eqmakebox[#1]{$\displaystyle#2$}}

\begin{document}

 \textbf{Théoriquement :}\\
On sait que l'expression mathématique d'une tension s'écrit sous la forme suivante :
\[ u(t)=U_m \cos(2\pi f t) \]
Pour que le signal modulant ait une expression mathématique, on pose $U_m=A\bigl(m\cos(2\pi f_s t)+1\bigr)$
\begin{align*}
-1&\leq \eqmathbox{\cos(2\pi f_s t)} \leq 1\\
-m&\leq\eqmathbox{ m\cos(2\pi f_s t)} \leq m\\
1-m&\leq \eqmathbox{m\cos(2\pi f_st)+1} \leq 1+m\\
A(1-m)&\leq \eqmathbox{A\bigl(m\cos(2\pi f_s t)+1\bigr)}\leq A(1+m)
\end{align*}

\end{document} 

enter image description here

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  • Oh that's exactly what I wanted, Thank you so much Bernard <3 – Eduardo.ni Feb 19 at 19:46
  • 1
    B.t.w., don't use the plain TeX construct $$ … $$ for unnumbered displayed equations, the spacing is not very good. Use the latex construct \[ … \] instead. – Bernard Feb 19 at 19:55
  • Ohhh Thanks for the advice Sir I appreciate it ! – Eduardo.ni Feb 19 at 19:57

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