Align and Multline Environments in LaTeX

\usepackage{amsmath}

\begin{align}
f(x) &= x^2 + 2x + 1 \\
g(x) &= \sin x + \cos x
\end{align}

\begin{multline}
A = a_1 + a_2 + a_3 + a_4 + a_5 + a_6 + a_7 \\
    + a_8 + a_9 + a_{10}
\end{multline}

\begin{equation}
\begin{split}
y &= (x+1)^2 \\
  &= x^2 + 2x + 1
\end{split}
\end{equation}