2倍角公式求值》cosπ/12 x cos5π/12

求值cos5π/8*cosπ8 不查表求值：cos5π/12·sinπ/12= cos5/12πcosπ/12+cosπ/12sinπ/6=? 计算cos5分之π+cos5分之2π+cos5分之3π+cos5分之4π (sin5π/12+cos5π/12)(sinπ/12-cosπ/12) (sin5π/12-sinπ/12)(cos5π/12+cosπ/12)=? 利用二倍角公式求值sin(π/12)cos(π/12) cos5π/12=sinπ/12 帮我解,证明恒等式（cos平方5π/12）+（cos平方π/12）+（cos5π/12）（cosπ/12）=5/4 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. 数学,证明恒等式（cos平方5π/12）+（cos平方π/12）+（cos5π/12）（cosπ/12）=5/4.