sin(α -π/4)=7√2/10,cos2α =7/25,求sianα 及tan(α +π/3)
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sin(α -π/4)=7√2/10,cos2α =7/25,求sianα 及tan(α +π/3)
cos2α =7/25=1-2sin^2a ,2sin^2a=1-7/25=18/25 ,sina=±3/5
sin(α -π/4)=(√2/2)(sina-cosa)=7√2/10 ,sina-cosa=7/5 ,cosa=4/5 ,tana=±3/4
tan(α +π/3)=(tana+tanπ/3)/(1-tanatanπ/3)
=(3/4+√3)/(1-3√3/4)或( -3/4+√3)/(1+3√3/4)
sin(α -π/4)=(√2/2)(sina-cosa)=7√2/10 ,sina-cosa=7/5 ,cosa=4/5 ,tana=±3/4
tan(α +π/3)=(tana+tanπ/3)/(1-tanatanπ/3)
=(3/4+√3)/(1-3√3/4)或( -3/4+√3)/(1+3√3/4)
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