sin3/7π*cos2/5π-cos(-3/7π)*sin(-2/5π)

已知(sinα+sin2α+sin3α)/(cosα+cos2α+cos3α)=﹣4/tanα,且π＜2α＜3π/2,求 cosπ/5*cos2π/5 =(2sinπ/5*cosπ/5*cos2π/5)/(2sinπ/5) =(sin2π/5 cosπ/3+tanπ/4+3tan²π/6+sinπ/2+cosπ+sin3π/2等于?. 三角函数的诱导公式.已知sin（θ-3/2π）+cos（3/2π+θ）=3/5求sin3（π/2 化简 (1)、sin(α+180度)cos(-α)sin(-α-180度) (2)、sin3(-α)cos(2π+α)t 已知cos2α=-7/25,2α属于(π,3π/2).求sinα,cosα 已知sinα+cosα=1/5,且π/2≤α≤3π/4,求cos2α 已知tana=2,计算①2cos(π/2+a)-cos(π-a))/sin(π/2-a)-3sin(π+a) ②sin3 COSπ/5乘以COS2π/5 求COSπ/5*COS2π/5 （二倍角的三角函数）cosπ/5cos2/5π的值是______cosπ/5cos2π/5 =sinπ/5cosπ/5c 已知sin^2α+√3sinαcosα-2cos^2a=0 α∈(π/6,5π/12)求sin(2α-π/3)和cos2