My equation split over two lines doesn't centre on the page

Question

I am trying to split an equation over two lines but when I do it doesn't centre in the middle of the page.

Here is my code:

\begin{subequation}
\begin{align}
\centering
    \begin{split}
      \textit{SOC}= \alpha + \beta_1\textit{Only languages} + \beta_2\textit{Languages with other subject} \\*+ \beta_3\textit{Social Sciences} + \beta_4\textit{STEM }+ \sum Y + \epsilon
    \end{split}
\tag{2B}
\end{align}
\end{subequation}

and this is what comes up:

Answer 1

There are many ways to split an equation over two lines and most have different justifications. The first way shown is what was in the question. There are two problems with this code. First the \centering is not needed and second the align environment is used but no align marks, &, are included so everything is automatically aligned to the right. Two other ways of splitting up an equation are multline (notice only one i, not multiline) and gather. For centering both parts you probably want gather.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
    With \verb|multline|
    \begin{subequations}
        \begin{multline}
            \textit{SOC}= \alpha + \beta_1\textit{Only languages} + \beta_2\textit{Languages with other subject} \\*+ \beta_3\textit{Social Sciences} + \beta_4\textit{STEM }+ \sum Y + \epsilon
            \tag{2B}
        \end{multline}
    \end{subequations}
    With \verb|gather|
    \begin{subequations}
        \begin{gather*}
            \textit{SOC}= \alpha + \beta_1\textit{Only languages} + \beta_2\textit{Languages with other subject} \\*+ \beta_3\textit{Social Sciences} + \beta_4\textit{STEM }+ \sum Y + \epsilon
            \tag{2B}
        \end{gather*}
    \end{subequations}
\end{document}

Note that the amsmath environment is subequations (with an s on the end) not subequation.