cos5/12πcosπ/12+cosπ/12sinπ/6=?

cosπ/12*cos5π/12结果是1/4 cos5/12πcosπ/12+cosπ/12sinπ/6=? 求值cos5π/8*cosπ8 (sin5π/12+cos5π/12)(sinπ/12-cosπ/12) (sin5π/12-sinπ/12)(cos5π/12+cosπ/12)=? 2倍角公式求值》cosπ/12 x cos5π/12 cos平方5π/12+cos平方π/12+cos5π/12cosπ/12的值等于多少（要过程） cos方5π/12+cos方π/12+cosπ/12*cos5π/12 最后等于5/4的过程. cos方5π/12+cos方π/12+cosπ/12*cos5π/12 最后等于4/5的过程. 帮我解,证明恒等式（cos平方5π/12）+（cos平方π/12）+（cos5π/12）（cosπ/12）=5/4 求值:cos5π/8cosπ/8= 求值cos5π/8cosπ/8解cos5π/8cosπ/8,请写出过程. 数学,证明恒等式（cos平方5π/12）+（cos平方π/12）+（cos5π/12）（cosπ/12）=5/4.help me!真的看不懂。 cos5π/3为什么等于1/2不是-1/2?cos5π/3=cos（5π/3-2π）=cos（-π/3）=-cosπ/3=-1/2不是这样的吗 cos(-π/12)过程 cosπ/12= sinπ/12cos5π/12等于 求cos5π/12sinπ/12