cos平方5π/12+cos平方π/12+cos5π/12cosπ/12的值等于多少(要过程)

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cos平方5π/12+cos平方π/12+cos5π/12cosπ/12的值等于多少(要过程)cos平方5π/12+cos平方π/12+cos5π/12cosπ/12的值等于多少(要过程)cos平方5

cos平方5π/12+cos平方π/12+cos5π/12cosπ/12的值等于多少(要过程)
cos平方5π/12+cos平方π/12+cos5π/12cosπ/12的值等于多少(要过程)

cos平方5π/12+cos平方π/12+cos5π/12cosπ/12的值等于多少(要过程)
cos(5π/12)^2+cos(π/12)^2+cos(5π/12)cos(π/12)
=sin(π/12)^2+cos(π/12)^2+sin(π/12)cos(π/12)
=1+sin(π/6)/2
=5/4