若sina:cos(a/2)=8:5,则cosa=有助于回答者给出准确的答案若sina:sin(a/2)=8:5,则cosa=
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若sina:cos(a/2)=8:5,则cosa=有助于回答者给出准确的答案若sina:sin(a/2)=8:5,则cosa=
若sina:cos(a/2)=8:5,则cosa=
有助于回答者给出准确的答案
若sina:sin(a/2)=8:5,则cosa=
若sina:cos(a/2)=8:5,则cosa=有助于回答者给出准确的答案若sina:sin(a/2)=8:5,则cosa=
sina=2sin(a/2)cos(a/2)
所以sina/cos(a/2) = 2sin(a/2)cos(a/2)/cos(a/2)=2sin(a/2)=8/5
sin(a/2)=4/5
cosa = 1-2[sin(a/2)]^2=1-2*(4/5)^2=1-2*16/25=-7/25
若sina:sin(a/2)=8:5,则cosa=
sina/sin(a/2) = 2sin(a/2)cos(a/2)/sin(a/2)=2cos(a/2)=8/5
cos(a/2)=4/5
cosa = 2[cos(a/2)^2]-1=2*(4/5)^2 -1=2*16/25 -1=7/25
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