If , then find the value of _ r=1 ^ 8 (rA)…

MATHEMATICS · Subjective · A Level · Mathematics · Trigonometry · Trigonometry

Problem

If A=π5A = \frac{\pi}{5}, then find the value of ∑r=18tan⁡(rA)⋅tan⁡((r+1)A).\sum_{r=1}^{8} \tan(rA) \cdot \tan((r+1)A).

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