cos五分之π 乘以cos五分之二π
cos五分之π 乘以cos五分之二π
数学人气：183 ℃时间：2019-09-17 14:21:11
优质解答
原式=2sin(π/5)cos(π/5)cos(2π/5)/[2sin(π/5)]=sin(2π/5)cos(2π/5)/[2sin(π/5)]=2sin(2π/5)cos(2π/5)/[4sin(π/5)]=sin(4π/5)/[4sin(π/5)]=sin(π-π/5)/[4sin(π/5)]=sin(π/5)/[4sin(π/5)]=1/4
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