If \( \mathrm{A}=\sin \frac{2 \pi}{7}+\sin \frac{4 \pi}{7}+\sin \frac{8 \pi}{7} \) and \( \mathr...

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If \( \mathrm{A}=\sin \frac{2 \pi}{7}+\sin \frac{4 \pi}{7}+\sin \frac{8 \pi}{7} \) and \( \mathrm{B}=\cos \frac{2 \pi}{7}+\cos \frac{4 \pi}{7}+\cos \frac{8 \pi}{7} \) then \( \sqrt{\mathrm{A}^{2}+\mathrm{B}^{2}} \) is equal to
(W)
(A) 1
(B) \( \sqrt{2} \)
(C) 2
(D) \( \sqrt{3} \)
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