sin(a π 3) sina=-4根号3 5

sin(a+π/3)+sina=(-4/5)*根号3展开左边,即√3sin(a+π/6)=(-4/5)*根号3∴sin(a+π/6）=-4/5∵-π/2再问：麻烦下左边的式子怎么拆开请帮下。。怎么得到

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

（sina+cosa)/(sina-cosa)=2所以sina=3cosa因为sina*sina+cosa*cosa=1,所以sina=3*根号10/10,cosa=根号10/10,或者sina=-3

sinacosπ/3+cosasinπ/3+sina=-4√3/5sina*3/2+cosa*√3/2=-4√3/5√3(sina*√3/2+cpsa*1/2)=-4√3/5sinasinπ/3+cp

sin(a+π/3)+sina=sinacos(π/3)+sin(π/3)cosa+sina=-4√3/5化简得到√3sina+cosa=-8/5再利用sina^2+cosa^2=1带入解得cosa再

因为sin(2π-a)=sina所以,sin(3π-a)=sin(π-a)=sina不懂的欢迎追问,再问：Thanks,那什么时候sina才可以换成cosa呢，再答：sin(π/2-a)=cosasi

证：左边=sina(cosa)³=sinacosa(cosa)²=(1/4)2sinacosa[2(cosa)²]=(1/4)sin(2a)[1+cos(2a)]=(1/

因为2π/3在Y轴负半轴上,则2π/3-a在第3象限上则sin(2π/3-a)=-cosa1-sin(2π/3-a)/sina=1+cosa/sina=1+cota

去括号啊sinπ+sina=1/3,sina=1/3-sinπ

sin(a-π/4)=3/5∴cos(a-π/4)=±4/5（1）cos(a-π/4)=4/5则sina=sin[(a-π/4)+π/4]=sin(a-π/4)*cos(π/4)+cos(a-π/4)

sinπ=0cosπ=-1所以sinπcosa+cosπsina=-sina

(1)展开,得sinAcosπ/4+cosAsinπ/4+sinAcosπ/4-cosAsinπ/4=2sinAcosπ/4=√2×sinA=√2/3所以,sinA=1/3.(2)原式=[sinAco

因为正弦函数周期2πsin(3π+θ)=sin（2π+π+θ）=sin（π+θ）,由诱导公式得：sin（π+θ）=-sinθ,下面应该没问题了吧

(tanπ/4+tana)/(1-tanπ/4tana)=3tanπ/4=1所以tana=1/2sina/cosa=tana=1/2cosa=2sina带入恒等式sin²a+cos²

sin(2π-a)=4/5sin(-a)=4/5sina=-4/5a∈(3/2π,2π),cosα＞0cosα=根号(1-sin^2α)=根号{1-16/25}=3/5（sina+cosa）/（sin

sin(a+π/4)cos(a+π/4)=(1/2)*sin[2(a+π/4)]=(1/2)*sin(2a+π/2)=(1/2)*cos(2a)=(1/2)*[1-2*(sina)^2]=(1/2)*

sin(3a)=sin(2a+a)=sin(2a)cosa+cos(2a)sina=(2sinacosa)cosa+(1-2sin^a)sina=2sina(1-sin^a)+sina-2sin^3a

sina+sin²a=1∴sina=1-sin²a=cos²a3cos^2a+cos^4a-2sina+1=3sina+sin²a-2sina+1=sina+1

sinA+sin(A+2π/3)+sin(A-2π/3)=sinA+sinAcos2π/3+cosAsin2π/3+sinAcos2π/3-cosAsin2π/3=sinA+2sinAcos2π/3=