[Tex/LaTex] Equivalence arrow in LaTeX

Question

I have an equation like

\documentclass[12pt,a4paper]{report}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsthm}
\begin{document}
\begin{align*}
 a+b+c+d+e+f&=g\\
\Leftrightarrow a &=g-a-b-c-d-e-f
\end{align*}
\end{document}

I'd like to have the arrow left to both equation, how do I do this?

Answer 1

Do you mean like this?

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\begin{alignat*}{2}
&\iff & a+b+c+d+e+f &=g             \\
&\iff &           a &=g-b-c-d-e-f
\end{alignat*}
\end{document}