aligning latex code example

Example 1: centering text latex

\documentclass{article}

\begin{document}

This is a really long sentence as an example.  The second have of this\\
\centerline{sentence should be centered.}
\end{document}

Example 2: latex align equation

\begin{align}
(a+b)^2 &= (a+b)(a+b) \\
        &= a^2+2ab+b^2 
\end{align}

Example 3: aligning latex

\begin{align*}
x&=y           &  w &=z              &  a&=b+c\\
2x&=-y         &  3w&=\frac{1}{2}z   &  a&=b\\
-4 + 5x&=2+y   &  w+2&=-1+w          &  ab&=cb
\end{align*}