# Aligning two equations on a selected pair of symbols

How can I center an equation according to \Leftrightarrow? I would like the second\Leftrightarrow to be below the first.

\documentclass[12pt,a4paper]{report}
\begin{document}

$$x = r \cos \varphi = 0 \qquad \Leftrightarrow \qquad \cos\varphi = 0,$$

$$y= 56 \qquad \Leftrightarrow \qquad \sin\alpha = ,$$

\end{document}

• I can't help but comment that if \Leftrightarrow is supposed to mean "if and only if", the statement in the first equatioin is incorrect: r\cos\varphi=0 is true if either \cos\varphi=0 or r=0. – Mico Dec 26 '18 at 14:03
• \Leftrightarrow can be replaced with \iff – user94293 Dec 26 '18 at 20:19

I suggest you

• replace the two equation enviroments with a single align environment, and
• insert & alignment points in front of the two \Leftrightarrow directives.

The align LaTeX environment is one of several tools the amsmath package provides for typesetting multi-line math constructs. It would be an excellent idea for you to familiarize yourself with the user guide of the amsmath package.

\documentclass[12pt,a4paper]{report}
\usepackage{amsmath} % for 'align' environment
\begin{document}
\begin{align}
\end{align}
\end{document}


Thank's to @Mico

\documentclass[12pt,a4paper]{report}
\usepackage{amsmath}
\begin{document}
\begin{align}
x = r \cos \varphi = 0 \qquad &\Leftrightarrow \qquad \cos\varphi = 0, \\