5 Use the triangle in Fig. 4 to prove that \(\sin ^ { 2 } \theta + \cos ^ { 2 } \theta = 1\). For what values of \(\theta\) is this proof valid?
\begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{64cb5e15-35b0-43a3-9f6d-f8e1c04b80b8-1_357_595_1831_798}
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\caption{Fig. 4}
\end{figure}