Mine

Working (but lame):

\begin{align*}
A(x) &= \binom{a-1}{0} + \binom{a-1}{1} x + \binom{a-1}{2} x^2 + \binom{a-1}{3} x^3 + \cdots \\
x \, A(x) &= \hspace{4.93em}\binom{a-1}{0} x + \binom{a-1}{1} x^2 + \binom{a-1}{2} x^3 + \cdots
\end{align*}

Not working:

\begin{align*}
A(x) &= \binom{a-1}{0} + &\binom{a-1}{1} x + &\binom{a-1}{2} x^2 + &\binom{a-1}{3} x^3 + \cdots \\
x \, A(x) &= &\binom{a-1}{0} x + &\binom{a-1}{1} x^2 + &\binom{a-1}{2} x^3 + \cdots
\end{align*}

and various variants