sin^4π/8 +cos^4π/8

化简sin(α-5π)/cos(3π-α)×cos(π/2-α)/sin(α-3π)×cos(8π-α)/sin(-α-4π) cos^6(π/8)-sin^6(π/8)=求值,[cos^2(π/8)-sin^2(π/8)][cos^4(π/8)+sin^4(π/8)+cos^2(π/8)sin^2(π/8)]=cos(π/4)[1-cos^2(π/8)sin^2(π/8)]=cos(π/4)[1-[sin^2(π/4)]/4]==7√2/16 sin^4π/8 +cos^4π/8 (cos(π/8))^4-(sin(π/8))^4 sin^4π/8-cos^4π/8=? cos^4(π/8)-sin^4(π/8)等于? cos^4π/8sin^4π/8等于cos^4π/8乘以sin^4π/8等于 化简：[1+2sin(α+2π)*cos(α-2π)]/[sin(α+4π)+cos(α+8π)] sinθcosθ=1/8,θ∈(π/4,π/2),求cosθ-sinθ的值 为什么-[cos²(π/8)-sin²(π/8)]=-cos(π/4) 若 sinθ ·cosθ=1/8,求 sinθ +cosθ?怎样用单位圆确定 sinθ 和cosθ大若 sinθ ·cosθ=1/8,求 sinθ +cosθ?怎样用单位圆确定 sinθ 和cosθ谁大谁小?θ属于（π/4，π/2），关键是怎样用单位圆比较大小 2sinπ/8cosπ/8怎么得到sinπ/4? 化简sin（a-5π）cos（-π/2-a）cos（8π-a）/sin（a-3π/2）sin（-a-4π） sin(θ-5π)cos[(-π/2)-θ]cos(8π-θ)}/sin[θ-(3π/2)]sin(-θ-4π)我晕，正的还是负的 化简sin（a-5π）cos（-π/2-a）cos（8π-a）/sin（a-3π/2）sin（-a-4π） 求SINπ/64 COSπ/64 COSπ/32 COSπ/16 COSπ/8 sinπ/8×cosπ/8 sinπ/8×cosπ/8