作业帮cos2π/7×cos4π/7×cos6π/7等于多少?3Q
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cos2π/7×cos4π/7×cos6π/7等于多少?3Q
cos2π/7×cos4π/7×cos6π/7等于多少?3Q
cos2π/7×cos4π/7×cos6π/7等于多少?3Q
原式=sinπ/7*cos2π/7*cos4π/7*-cosπ/7/sinπ/7 =-1/2sin2π/7*cos2π/7*cos4π/7/sinπ/7 =-1/4sin4π/7*cos4π/7/sinπ/7 =-1/8sin8π/7/sinπ/7 =1/8sinπ/7/sinπ/7 =1/8