Aligning equation to the left

alignmentequations

I'm trying to have all my equation aligned to the left of the document instead of the center. I'm trying with flalign but fore some strange reason I get this :

enter image description here

Here is the code :

\documentclass[11pt, french]{article} %article report  book  letter  slides
\usepackage{blindtext}
\usepackage{geometry}
 \geometry{
 a4paper,
 total={170mm,257mm},
 left=20mm,
 top=20mm,
 }
\usepackage[french]{babel}
\selectlanguage{french}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{esint}
\begin{document}
\newcommand{\prt}[2]{\frac{\partial #1}{\partial #2}}

\begin{flalign}
C_x = C_{x_0} + k{C_z}^2 && \\
\prt{f}{C_z} = \frac{0.015+\frac{{C_z}^2}{20}-\frac{{C_z}^2}{10}}{\left( 0.015+{C_z}^2 \right)^2}&&\\
\prt{f}{C_z} = 0 \Leftrightarrow C_{x_0} + k{C_z}^2 - 2k{C_z}^2 = 0 \Leftrightarrow C_z = \sqrt{\frac{C_{x_0}}{k}} = 0,548 &&\\
C_x = 0.015 + \frac{1}{20} * 0.548^2 = 0.03&&\\
f = \frac{0.548}{0.03} = 18,26 &&
\end{flalign}

\end{document}

How can I fix my problem?

Best Answer

enter image description here

Use [fleqn] to get equations flush left, and use gather not align as you are not aligning on =

\documentclass[11pt, french,fleqn]{article} %article report  book  letter  slides
\usepackage{blindtext}
\usepackage{geometry}
 \geometry{
 a4paper,
 total={170mm,257mm},
 left=20mm,
 top=20mm,
 }
\usepackage[T1]{fontenc}
\usepackage[french]{babel}
\selectlanguage{french}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{esint}
\begin{document}
\newcommand{\prt}[2]{\frac{\partial #1}{\partial #2}}

\begin{gather}
C_x = C_{x_0} + k{C_z}^2  \\
\prt{f}{C_z} = \frac{0.015+\frac{{C_z}^2}{20}-\frac{{C_z}^2}{10}}{\left( 0.015+{C_z}^2 \right)^2}\\
\prt{f}{C_z} = 0 \Leftrightarrow C_{x_0} + k{C_z}^2 - 2k{C_z}^2 = 0 \Leftrightarrow C_z = \sqrt{\frac{C_{x_0}}{k}} = 0,548 \\
C_x = 0.015 + \frac{1}{20} * 0.548^2 = 0.03\\
f = \frac{0.548}{0.03} = 18,26 
\end{gather}

\end{document}
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