已知cosα=-1/5,π/2<α<π,则sinα/2等于___(
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已知cosα=-1/5,π/2<α<π,则sinα/2等于___(
已知cosα=-1/5,π/2<α<π,则sinα/2等于___(
已知cosα=-1/5,π/2<α<π,则sinα/2等于___(
π/4<a/2<π/2
锐角,sina/2>0
cosa=1-2sin²(a/2)=-1/5
即sin²(a/2)=3/5
sina/2=√15/5
π/2<α<π
π/4<α/2<π/2
√2
sin^2(α/2)=3/5
sinα/2=√3/5=(√15)/5