cosπ/9cos2π/9cos3π/9cos4π - 知识问答

cosπ/9cos2π/9cos3π/9cos4π/9=

1个回答

(cosπ/9)(cos2π/9)(cos3π/9)(cos4π/9)
=(sinπ/9)(cosπ/9)(cos2π/9)(cosπ/3)(cos4π/9)/(sinπ/9)
=(sin2π/9)(cos2π/9)(cos4π/9)/[4(sinπ/9)]
=(sin4π/9)(cos4π/9)/[8(sinπ/9)]
=(sin8π/9)/[16(sinπ/9)]
=(sinπ/9)/[16(sinπ/9)]
=1/16

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