来自白莉媛的问题
已知sina=2sinb,tana=3tanb,则cos2a=
已知sina=2sinb,tana=3tanb,则cos2a=
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2020-06-24 09:27
已知sina=2sinb,tana=3tanb,则cos2a=
已知sina=2sinb,tana=3tanb,则cos2a=
sina=2sinb,∴sinb=(1/2)sinatana=3tanb∴tanb=(1/3)tana∵tan²b=sin²b/cos²b=sin²b/(1-sin²b)∴(1/9)tan²a=(1/4)sin²a/[1-(1/4)sin²a](1)sin²a=0,此时cos...