3

This question already has an answer here:

How to typeset this equation?

enter image description here

Please help me.

marked as duplicate by Werner, AboAmmar, Henri Menke, TH., Stefan Pinnow Jun 6 '17 at 4:14

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

2

Here you go:

\documentclass{memoir}
\usepackage{amsmath}

\begin{document}

\begin{align*}
    \text{simult\'aneas:}
    \quad
    \begin{cases}
    2x+y=3\\
    2x-y=1\\
    \end{cases}
    \quad
    \Leftrightarrow
    \quad
    x=1,~y=1
\end{align*}


\begin{align*}
    \text{simult\'aneas:}
    \quad
    \begin{cases}
    2x+y=3\\
    2x-y=1\\
    \end{cases}
    \quad
    \Leftrightarrow
    \quad
    x=y=1
\end{align*}

\begin{align*}
    \text{simult\'aneas:}
    \quad
    \begin{cases}
    2x+y=3\\
    2x-y=1\\
    \end{cases}
    \quad
    \Leftrightarrow
    \quad
    \begin{cases}
    x=1\\
    y=1\\
\end{cases}\end{align*}

\end{document}

enter image description here

You might want to change \text to \textsf.

This might be considered a beginner's question, so you might want to have a look on What are good learning resources for a LaTeX beginner?.

  • this is really a one-line display, so equation* would be more appropriate than align*. – barbara beeton Jun 6 '17 at 0:43

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