# How to align multiple equations

I want to align multiple equations and two "conditions".

\begin{align}
\begin{split}
||\pmb{x}||_p &= \left(\sum_i |x_i|^p\right)^{\frac{1}{p}} \label{formel:pnorm}\\
p & \in \mathbb{R}\\
p & \geq 1 \\
\end{split} \\
||\pmb{x}||_1 &= \sum_i |x_i|\label{formel:1norm} \\
||\pmb{x}||_\infty &= \max_i |x_i|\label{formel:maxnorm}
\end{align}


Now:

Removing the \\ in the last line of split.

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
\begin{align}
\begin{split}
\lVert\pmb{x}\rVert_p &= \left(\sum_i \lvert x_i\rvert^p\right)^{\frac{1}{p}} \label{formel:pnorm}\\
p & \in \mathbb{R}\\
p & \geq 1
\end{split} \\
\lVert\pmb{x}\rVert_1 &= \sum_i \lvert x_i\rvert\label{formel:1norm} \\
\lVert\pmb{x}\rVert_\infty &= \max_i \lvert x_i\rvert\label{formel:maxnorm}
\end{align}
\end{document}


I propose a different layout with alignat, and some improvement:

\documentclass{article}
\usepackage{mathtools}
\usepackage{amssymb, bm}

\begin{document}

\begin{alignat}{2}
\lVert\bm{x}\rVert_p &= \Bigl(\sum_i \lvert x_i\rvert^p\Bigr)^{\!\frac{1}{p}\!} \label{formel:pnorm} & \qquad (p \in \mathbb{R},\: p\ge 1) \\
\lVert\bm{x}\rVert_1 &= \sum_i \lvert x_i\rvert\label{formel:1norm} \\
\lVert\bm{x}\rVert_{\mkern-1.5mu\mathrlap{\infty}\,\hphantom{1}} &= \max_i \lvert x_i\rvert\label{formel:maxnorm}
\end{alignat}

\end{document}