12 Fig. 12 shows a rhombus OACB in an Argand diagram. The points A and B represent the complex numbers \(z\) and \(w\) respectively.
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\includegraphics[alt={},max width=\textwidth]{82808722-0abc-411a-9aa3-c0f368a4c95e-4_641_659_1201_242}
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\caption{Fig. 12}
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Prove that \(\arg ( z + w ) = \frac { 1 } { 2 } ( \arg z + \arg w )\).
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[A copy of Fig. 12 is provided in the Printed Answer Booklet.]