Find the Error!

\begin{align*}
1+\cos(x) & = 1 + (1-\sin^2(x))^{1/2} \\
(1+\cos(x))^2 & = \left\{1 + (1-\sin^2(x))^\frac{1}{2}\right\}^2 \\
\end{align*}
Let $x=\pi$.