cos81*cos36+cos9*cos54=?

cos81*cos36+cos9*cos54=? sin21°cos81°-sin69°cos9° sin21度cos81度-sin69度cos9度=? 求值：sin21°cos81°-sin69°cos9° cos54°cos9°+sin54°cos81° sin21°cos81°+sin69°cos9°化简要详解 4（sin18°）平方+4（cos36°）平方4sin²18°+4cos²36°=4sin²18°+4(1-sin²36°)=4-4(sin²36°-sin²18°)=4-4(sin36°+sin18°)(sin36°-sin18°)=4-4*2sin27°cos9°*2cos27°sin9°=4-4*(2sin27°cos27°)*(2sin9°cos9°)=4- cos36度=2cos方18度+1,什么地方错了, 2cos9π/13*cosπ/13=[cos(9π/13+π/13)+cos(9π/13-π/13)]怎么化? cos9/π.cos9/2π.cos9/3π.cos9/4π等于多少! sin9+cos15sin6/cos9-sin15sin6 2cos9/13πcosπ/13+cos5/13π+cos3/13π的解法?我有一个儿子,作为母亲的我无力解决, 2cos9π/13cosπ/13=cos10π/13+cos8π/13,这是怎么换算过来的啊如题. 为什么cos24度cos36度-cos66度cos54度这么算cos24度cos36度-cos66度cos54度=cos24 cos36 - sin24 sin36=cos (24+36)=cos 60=1/2很多人都这么算那个cos66度 和cos54度上哪去了 cos36和cos36度有区别吗? cos36和cos36度有区别吗? sin57-sin33+2√2cos81*sin69 cos9分之派cos9分之2派cos9分之4派等于多少?