已知sin(α+π/4)=1/2.α∈(π/2,π),求sin2α,cos2α,tan2α
人气：118 ℃ 时间：2019-12-24 20:45:13
解答
sin(α+π/4)=1/2则cos(α+π/4)=-[√1-(1/2)^2]=-(√3)/2α∈(π/2,π)且α+π/4∈(π/2,π)则2α∈(π,3π/2)sin(2α+π/2)=2sin(α+π/4)cos(α+π/4)=-(√3)/2cos2α=-(√3)/2sin2α=-1/2tan2α=(√3)/3...
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