15ãf(x)=â3sin(x+Ï/2)-sin(x+Ï)=sinx-â3cosx=2sin(x-Ï/3)ï¼
(1)ãæå°æ£å¨æT=2Ïï¼
(2)ãg(x)=2sin(x-Ï/6-Ï/3)=-2cosxï¼xâ[0,Ï]ï¼
ââãg(x)max=2ï¼g(x)min=-2ï¼
16ãαâ(0,Ï/4)ï¼ââã2αâ(0.Ï/2)ï¼
(1)ã(sinα+cosα)^2=1+sin2α=9/5ï¼ââãsin2α=4/5ï¼
ââãcos2α=â(1-sin^22α)=3/5ï¼
ââãtan2α=4/3ï¼
(2)ãβâ(Ï/4,Ï/2)ï¼ââãβ-Ï/4â(0,Ï/4)ï¼2βâ(Ï/2.Ï)ï¼
sin(β-Ï/4)=3/5ï¼ââãcos(β-Ï/4)=4/5ï¼
ââã2sin(β-Ï/4)cos(β-Ï/4)=sin(2β-Ï/2)=-cos2β=24/25ï¼
ââãcos2β=-24/25ï¼
ââãsin2β=â(1-cos^22β)=7/25ï¼
sinα+cosα=3â5/5ï¼sinαcosα=2/5ï¼tanα<1
ââãsinα<cosαï¼
ââãsinα=â5/5ï¼cosα=2â5/5
ââãcos(α+2β)=cosαcos2β-sinαsin2β=-11â5/25ã
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