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sinα/2=-根号3/3
α/2=-arcsin(根号3/3)=2π-arcsin(根号3/3)
α=4π-2arcsin(根号3/3)=2π-2arcsin(根号3/3)
cosα=cos(2π-2arcsin(根号3/3))=cos(-2arcsin(根号3/3))
=cos(2arcsin(根号3/3))=1-2sin^2(arcsin(根号3/3))=1-2*(1/3)
=1-2/3=1/3
α/2=-arcsin(根号3/3)=2π-arcsin(根号3/3)
α=4π-2arcsin(根号3/3)=2π-2arcsin(根号3/3)
cosα=cos(2π-2arcsin(根号3/3))=cos(-2arcsin(根号3/3))
=cos(2arcsin(根号3/3))=1-2sin^2(arcsin(根号3/3))=1-2*(1/3)
=1-2/3=1/3
1年前
10
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