Alinear ecuación multilínea

Question

Lo intenté aligny alignattambién, pero no puedo obtener la alineación adecuada para mi grupo de ecuaciones. El problema está en la segunda línea, que es la segunda parte de la primera ecuación. Quiero que vaya más a la derecha, algo así como multlinela salida del entorno.

\documentclass{article}
\usepackage{amsmath}  
\begin{document}  
\begin{align}
f_{X_{1},\ldots,X_{n}}(x_{1},\ldots,x_{n};\boldsymbol{\theta})&=f_{X_{n}|X_{n-1},\ldots, X_{1}}&&(x_{n}|x_{n-1},\ldots, x_{1},\boldsymbol{\theta}) \nonumber \\  
&&f_{X_{1},\ldots, X_{n-1}} (x_{1},\ldots, x_{n-1};\boldsymbol{\theta}) \nonumber \\
&=f_{X_{1}}(x_{1};\boldsymbol{\theta}) \prod_{t=2}^{n} f_{X_{t}|X_{t-1},\ldots,X_{1}}(x_{t}|x_{t-1},\ldots,x_{1};\boldsymbol{\theta}).
\end{align}
\end{document}

Answer 1

Utilice uno de estos:

 \documentclass{article}
    \usepackage{mathtools}

    \begin{document}

    \begin{align}
    f_{X_{1},\ldots,X_{n}}(x_{1},\ldots,x_{n};\boldsymbol{\theta})&= \begin{multlined}[t]f_{X_{n}|X_{n-1},\ldots, X_{1}}(x_{n}|x_{n-1},\ldots, x_{1},\boldsymbol{\theta})\\
  \times f_{X_{1},\ldots, X_{n-1}} (x_{1},\ldots, x_{n-1};\boldsymbol{\theta})\end{multlined} \nonumber \\
    &=f_{X_{1}}(x_{1};\boldsymbol{\theta}) \prod_{t=2}^{n} f_{X_{t}|X_{t-1},\ldots,X_{1}}(x_{t}|x_{t-1},\ldots,x_{1};\boldsymbol{\theta}).
    \end{align}


    \begin{align}
    f_{X_{1},\ldots,X_{n}}(x_{1},\ldots,x_{n};\boldsymbol{\theta})&= \begin{aligned}[t]f_{X_{n}|X_{n-1},\ldots, X_{1}}(x_{n}|x_{n-1},\ldots, x_{1},\boldsymbol{\theta})\\
  \times f_{X_{1},\ldots, X_{n-1}} (x_{1},\ldots, x_{n-1};\boldsymbol{\theta})\end{aligned} \nonumber \\
    &=f_{X_{1}}(x_{1};\boldsymbol{\theta}) \prod_{t=2}^{n} f_{X_{t}|X_{t-1},\ldots,X_{1}}(x_{t}|x_{t-1},\ldots,x_{1};\boldsymbol{\theta}).
    \end{align}

    \end{document}