How can I align all my equations to the left? [duplicate]

Question

This is my code but I want it to align to the left, more like the second part.

\documentclass{article}
\usepackage{mathtools}

\begin{document}
\begin{gather*}
    \sum F_x = 0 \\
    F_{Ax}+F_{AF}+F_{BF}\cos(30)= 0
    \\ 
    \\
    \sum F_y = 0 \\ 
    F_{Ay}+F_{BF}\sin(30) = 0
\end{gather*}


\end{document}

Answer 1

Welcome to TeX.SE... As you are not providing full MWE, I assumed that you are using one of a LaTeX standard class file book, here is the modified MWE:

\documentclass{book}
\usepackage[fleqn]{mathtools}
\begin{document}

\begin{gather*}
    \sum F_x = 0 \\
    F_{Ax}+F_{AF}+F_{BF}\cos(30)= 0
    \\ 
    \\
    \sum F_y = 0 \\ 
    F_{Ay}+F_{BF}\sin(30) = 0
\end{gather*}
\end{document}