sina^2 cos^2(π 6 a) 1 2sin(2a π 6)

2sin(A/2)·cos(π/2-A/2)=3/42[sin(A/2)]^2=3/41-cosA=3/4cosA=1/4sinA=±√15/4

[sin(2A+B)]/sinA-2cos(A+B)=[sin(A+B+A)]/sinA-2cos(A+B)=[sin(A+B)cosA+cos(A+B)sinA]/sinA-2cos(A+B)=[s

错了cos(A-π/2)=sinA

a-π/60＜a-π/6＜π/2cos(a-π/6)=4/5sin(a-π/6)=3/5;sina=sin(a-π/6)cosπ/6+cos(a-π/6)sinπ/6=3/5*√3/2+4/5*1/2

题中的2cos^a/2不明白!再问：2cos^2(a\2)不好意思，打漏了！再答：tan2a=2tana/(1-tan^2a)=2√2，a∈(π/2,π),tana

sina=2/3,a属于（π/3,π）,cosa

sin(a-π/4)]/cos(π+2a)=√2,√2/2(sina-cosa)=-√2cos2a,sina-cosa=-2(cos^2a-sin^2a),sina-cosa=2(sina+cosa)

cos(a-π/2)=cos-(π/2-a)=cos(π/2-a)=sina

这个根据sin和cos的图像来做.sin(sina)=sin(cosa）＜cos(a)＜cos(sina)=cos(cosa)要步骤可以来问我再问：步骤是什么啊。。。拜托详细点再答：哎呀我都忘了。。想

cos(3pi/2+a)=cos(3pi/2)cosa-sin(3pi/2)sina=0Xcosa-(-1)Xsina=sina,得证

我来第一题吧3(sina+cosa)^4+6(sina-cosa)^2+4(sin^6a+cos^6a)=3(sina+cosa)^2*(sina+cosa)^2+6(sin^2a+cos^2a-2s

sina+cosa=1/2,那么1+2sinacosa=1/4所以sinacosa=-3/8cosa/sina+sina/cosa=1/（sinacosa）=-8/3

Sin^4a+Sina*Cosa+Cos^2a=(sin^2a)^2+1/2sin2a+1/2(1+cos2a)=[(1-cos2a)/2]^2+1/2sin2a+1/2cos2a+1/2=1/4(1

（cos^2a/sina+sina）*tana=(1-2sin^2a)/sina+sina）*tana=((1/sina-2sina)+sina）*tana=(1/sina(1-sin^2a)）*si

sinA+sin（A+2/3π）+cos（A+5/6π）=sina+sinacos2/3pai+sin2/3paicosa+cosacos5/6pai-sinasin5/6pai=sina-1/2si

(sina+cosa)/(tan^2a-1)=(sina+cosa)/(sin^2a/cos^2a-cos^2a/cos^2a)=(sina+cosa)/((sin^2a-cos^2a)/cos^2a

cos(π/2+a）=cosπ/2cosa-sinπ/2sina=-sinacosπ/2=0,sinπ/2=1

tan4分之π=1所以(1+tana)/(1-tana)=1/22+tana=1-tanatana=-1/3原式=sinacosa/2cos²a-cos²a/2cos²a

证：(1-cos^2a)/(sina-cosa)-(sina+cosa)/(tan^2a-1)=sin^2a/(sina-cosa)-(sina+cosa)/（sin^2a/cos^2a-cos^2a

sina=-2cosasin(a-3π）+cos（π-a)/sin（-a)-cos(π+a）=(-sina-cosa)/(-sina+cosa)=(2cosa-cosa)/(2cosa+cosa)=1