Question

Please answer ... see the attachment

Answer 1

$\sin\theta1 + \sin\theta2 + \sin\theta3 = 3 \\ the \: only \: possibility \: is \\ \sin\theta1 = \sin\theta2 = \sin\theta3 = 1\\ \: \theta1 = \theta2 = \theta3 = \frac{\pi}{2} \\ now \cos\theta1 + \cos\theta2 + \cos\theta3 \\ = \cos \frac{\pi}{2} + \cos \frac{\pi}{2} + \cos \frac{\pi}{2} \\ = 0 + 0 + 0 \\=0$

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