高一数学题三角函数4题
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cos\u51fd\u6570\u57280\u5230\u6d3e\uff0f2\u533a\u95f4\u5185\u662f\u5355\u51cf\u51fd\u6570\uff0c0.75\u5ea6\u5c0f\u4e8e0.75\uff0c\u6240\u4ee5\u4e2d\u95f4\u663e\u7136\u662f>
tan\u51fd\u6570\u57280\u5230\u6d3e\uff0f2\u533a\u95f4\u662f\u5355\u589e\u51fd\u6570\uff0c1.2\u5ea6\u5c0f\u4e8e1.2\uff0c\u6240\u4ee5\u4e2d\u95f4\u5e94\u4e3a<
\u82e5\u4f7f\u7528\u8ba1\u7b97\u5668
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\u82e5\u4e3a\u5361\u897f\u6b27\u7cfb\u5217\u8ba1\u7b97\u5668\uff0cmode\u2014\u2014RDG\u4e2d\u5207\u6362\uff0cr\u4e3a\u5f27\u5ea6\u5236\uff0cd\u4e3a\u89d2\u5ea6\u5236
\uff081\uff09sinacosa=sin2a/2=tana/(1+tana^2)=3/2/(1+(3/2)^2)=6/13
\uff082\uff09\u56e02k\u03c0-\u03c0/4<=a<=2k\u03c0+\u03c0/4\uff0c\u6240\u4ee5|sina|<=cosa
\u6240\u4ee5\u539f\u5f0f=\u221a(sina-cosa)^2+\u221a(sina+cosa)^2=(cosa-sina)+(sina+cosa)=2cosa
\uff083\uff09(1+sina)/cosa=-1/2\uff0c
cosa/(sina-1)=cosa(1+sina)/((sina-1)(1+sina))=cosa(1+sina)/-cosa^2=-(1+sina)/cosa=1/2
\uff084\uff09\u770b\u4e0d\u6e05
sina=-3/5,tana=3/4
2.tana=-√3,a在第二或第四象限
若a在第二象限，sina>0,cosa<0,则sina=√3/2,cosa=-1/2
若a在第四象限，sina<0,cosa>0,则sina=-√3/2,cosa=1/2
3.sina=0.35,a在第一或第二象限
若a在第一象限，cosa>0,tana>0,则cosa=0.94,tana=0.37
若a在第二象限，cosa<0,tana<0,则cosa=-0.94,tana-=0.37
4.(1)cosatana=cosa*sina/cosa=sina
(2)（1-2sin²a）/ ( 2cos²a-1）=cos2a/cos2a=1
前三题的符号问题记住这个口诀：一全正，二正弦，三两切，四余弦。是每个象限里符号为正的。
第四题灵活运用定义和公式
1、sin a=-3/5,tan a=3/4
2、sin a=根号3/2,cos a=-1/2或者sin a=-根号3/2,cos a=1/2
3、sin a=0.33 cos a=0.94或sin a=-0.33 cos a=-0.94
4、1、=sinθ,2、=1
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