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#1
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⨷ÂìµÃÕ⡳¤Ñº (͹ءÃÁ cos)
cos(4Pi /15)+cos(8Pi /15)+cos(16Pi /15)+cos(32Pi /15) ¤Ô´Âѧä§ÍФѺ
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#2
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ÍéÒ§ÍÔ§:
1. $\frac{\pi}{3} - \frac{\pi}{5} = \frac{2\pi}{15}$ 2. $\cos(A - B) = \cos A \cos B + \sin A \sin B$ 3. $\cos A - \cos B = -2\sin\frac{A+B}{2} \sin \frac{A-B}{2}$ 4. $\sin (\pi/2 - A) = \cos A$ 5. $2\sin A \cos A = \sin 2A$ |
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