center equation latex code example

Example 1: latex align equation

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

Example 2: latex eqnarray centering

\begin{eqnarray*}
    &x + (y - 2)^4 = w^2 \\
    &(x  - 9)^2 + y_2^2 = w^2 \\
    &x + (y - 2)^4 = w^2 = (x  - 9)^2 + y_2^2 \\
\end{eqnarray*}