consecutivemath.tex

\documentclass{sample}
\begin{document}
\[
    x + y = z\\
    x = z - y
\]

or

\[
    x+y=z
\]
\[
    x=z-y
\]

or

\begin{align*}
    x+y=z\\
    x=z-y
\end{align*}
\end{document}