I am trying to left-align some equations so they line up nicely.
I'm using align with [fleqn] per this question and setlength per this question. But it doesn't seem to have worked. I tried the fleqn environment too per this question but it didn't do the trick either.
\documentclass{article}
\usepackage[fleqn]{mathtools}
\setlength{\mathindent}{0pt}
\begin{document}
\begin{align*}
A\triangleright B\triangleright A & \iff & x'Ax\geq x'Bx\cap x'Bx\geq x'Ax\forall x\\
& \iff & x'Ax=x'Bx\cap x'Bx=x'Ax\forall x\\
& \iff & x'Ax=x'Bx\forall x\\
& \iff & x'Ax-x'Bx=0\forall x\\
& \iff & x'(A-B)x=0\forall x
\end{align*}
\end{document}


alignenvironment inside\[...\]. – Mico Jan 29 '16 at 02:22