center an equation latex code example

Example: 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*}