若sin(2π 3-a) sina=4根号3 5,则sin(a 7π 6)的值为

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

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

(3sina+cosa)/(3cosa-sina)=23sina+cosa=6cosa-2sina5sina-5cosa=0tana=12-3sin(a-3π)sin(3π/2-a)-cos^2(-a

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

cos(a+B)*cosa+sin(a+B)*sina=-4/5得到cos[(a+b)-a]=-4/5...cosb=-4/5...sin(π/2-b)=cosb=-4/5

诱导公式：sin(a-2π)=sina,sin(π+a)=-sina也可以画图看：sin就是角对应射线在半径为1的圆上交点的纵坐标-2π就是把角顺时针转一圈,还是原位置,sin不变+π是逆时针转半圈,

sinA+sin(120-A)=3/2A=30°看出来的.

(sina+cosa)/(sina-cosa)=2sina=3cosasina=3/√10cosa=1/√10或者sina=-3/√10cosa=-1/√10sin(a-5π)*sin(3π/2-a)

因为sina+cosa=2sina-2cosa,则sina=3cosa,又因为sina+cosa=1则cosa=1/10,所以原式=sin(a-π-2π)[-sin(π/2-a)]=sin(a-π)(

证明：因为(sinA)^2+[sin(A+2π/3)]^2+[sin(A-2π/3)]^2=(sinA)^2+[sinAcos120度+sin120度cosA]^2+[sinAcos120度-sin1

sina+f(a)=2/3sina+sin(a+π/2)=2/3sina+sin(-a+π/2)=2/3sina+cosa=2/31+2sinacosa=4/92sinacosa=-5/9(√2sin

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

(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

/>∵sina=15/17,a∈（π/2,π)∴cosa=-√(1-sin²a)=-8/17∴sin(π/3+a)=sin(π/3)cosa+cos(π/3)sina=(1/2)√3×(-8

∵sina=15/17,a∈（π/2,π)∴cosa=-√(1-sin²a)=-8/17∴sin(π/3+a)=sin(π/3)cosa+cos(π/3)sina=(1/2)√3×(-8/1

f(x)=(2cos^2a/2-sina-1)/(sin(a+π/3)sin(a-π/3)=4(cosa-sina)/(sin^2a-3cos^2a)求啥?

由(sina+cosa)/(sina-cosa)=2,得sina=3cosa,即tana=3.sin(a-5π)*sin(3π/2-a)=（-sina）*（-sin（π/2-a））=(sina*cos

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

sina+cosa=2sina-2cosasina=3cosa代入恒等式sin²a+cos²a=1cos²a=1/10原式=sin(a-π)(-cosa)=-sina(-