搜搜做题作业网已知cos(a-π 6) sina=4根号下3 5,则sin(a 7π 6)=
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2sin(A/2)·cos(π/2-A/2)=3/42[sin(A/2)]^2=3/41-cosA=3/4cosA=1/4sinA=±√15/4
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
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/6)+sina=4√3/5展开cosacosπ/6+sinasinπ/6+sina=4√3/5√3/2*cosa+3/2*sina=4√3/51/2*cosa+√3/2*sina=4/
cos(a-π/2)=cos-(π/2-a)=cos(π/2-a)=sina
根据:cos（a-π/6）+sina=（4*根号3）/5有:cosacosπ/6+sinasinπ/6+sina=（4*根号3）/5(根号3)/2cosa+3/2sina=（4*根号3）/5得到:co
角A的范围是π到3π/2的开区间,即不包含两个端点
（4+3√3）/10
cosacosπ/6+sinasinπ/6+sina=4/5√3√3/2cosa+1/2sina+sina=4/5√3√3/2cosa+3/2sina=4/5√31/2cosa+√3/2sina=4/
cos(a-π/6)+sina=cosacosπ/6+sinasinπ/6+sina=(√3/2)cosa+(3/2)sina=4√3/5∴(1/2)cosa+(√3/2)sina=4/5sin(x+
sina+cosa=1/2,那么1+2sinacosa=1/4所以sinacosa=-3/8cosa/sina+sina/cosa=1/（sinacosa）=-8/3
tan4分之π=1所以(1+tana)/(1-tana)=1/22+tana=1-tanatana=-1/3原式=sinacosa/2cos²a-cos²a/2cos²a
cosa=-4/5cos(π/4-a)展开即根号2/2*(3/5-4/5)答案为-根号2/10（负的十分之根号二）
sina=-2cosasin(a-3π）+cos（π-a)/sin（-a)-cos(π+a）=(-sina-cosa)/(-sina+cosa)=(2cosa-cosa)/(2cosa+cosa)=1
2tana×sina=32sin^2a-3cosa=02cos^2a+3cosa-2=0(2cosa-1)(cosa+2)=0cosa=1/2,a=-π/3,cosa=-2(舍）cos（a-π/6）=
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)*