4 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]{9857ad89-b315-4cd6-8d8d-26a509ca52a8-2_362_606_906_772}
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\caption{Fig. 4}
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