a∈[0 2pai]sin45=2根3
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解析:∵sin(π-a)cos(-8π-a)=sinacosa=60/169即2sinacosa=120/169,又(sina)^2+(cosa)^2=1∵π/4<a<π/2,∴0<cosa<sina
设sin(pai/6+a)=sinX=1/3∴cos(2pai/3-2a)=cos(π﹣pai/3-2a)=﹣cos(pai/3﹢2a﹚=﹣cos2X∵cos2X=1﹣2sin²X=1﹣2/
f(a)=sinacosacota(-tana)/sina=-cosa
(a-a/a-1)÷a²+a/a-1=1/(a-1)*[(a-2)/a+a]=1/(a-1)*[(a-1)(a+2)/a]=1+2/aa=根号2sin45°+2=1+2=3(a-a/a-1)
解sin(π/2+a-π/4)sin(π/4-a)=cos(a-π/4)sin(π/4-a)=cos(π/4-a)sin(π/4-a)=1/6∴sin[2(π/4-a)]=1/3即sin(π/2-2a
sina=-3/5,a∈(pai,3pai/2)cosa小于0(sina)^2+(cosa)^2=1cosa=-4/5cos(a-pai/4)=cosacos(pai/4)+sinasin(pai/4
cos(2pai/3+2a)=2cos^2(pai/3+a)-1=2*(-1/2)^2-1=-1/2再问:2cos^2(pai/3+a)-1这里不是很明白。再答:这个是倍角公式cos2a=2cos^2
-7/9COS(2π/3+2a)=2cos(π/3+a)^2-1=-7/9
-1/7cos(3π/2-a)=-sina=2√5/5,sina=-2√5/5因为a∈(π,3π/2)所以a在第三象限所以cosa=-√5/5sin2a=2sina×cosa=4/5cos2a=2(c
a属于(π/2,π)sina>0cosa
诱导公式f(a)=sinacosacota/(-cosa)=-sinacota=-sina(cosa/sina)=-cosa所以f(-31π/3)=-cos(-31π/3)=-cos(31π/3)=-
再问:谢谢了再答:没事
a=sinpai/6=1/2b=cospai/6=√3/2a^2-ab-b^2=1/4-√3/4-3/4=-(2+√3)/4
tan(pai+a)=2tan(a)=2【sin(a-pai)+cos(pai-a)】/【sin(pai+a)-cos(pai+a)】=【-sin(a)-cos(a)】/【-sin(a)+cos(a)
sin(a-pai/2)=cosa错cos(a-pai/2)=sina对tan(a-pai/2)=cota错cot(a-pai/2)=tana错
sina=3/5,a∈(pai/2,pai),∴cosa=-4/5sin(a-pai/4)=1/根号(2)*(sina-cosa)=7根号(2)/10tan2a=sin2a/cos2a=2*sina*
你说的很对,来看看没有回答的问题,看到了你的这道题非常容易,怎么没人应答呢!tanatan(a+π/3)=2,求cos(2a+π/3)cos(2a+π/3)=cosacos(a+π/3)-sinasi
sin(pai-a)cos(2pai-a)sin(-a+3/2pai)/tan(-a-pai)sin(-pai-a)=sinacosa(-cosa)/(-tana*sina)=(cosa)^2/tan