已知tan(派-a)=-2,求3sina+2cosa\5sina-cosa 求sina•cosa
人气:274 ℃ 时间:2020-05-13 19:18:14
解答
tan(派-a)=-2=>tana=2
(3sina+2cosa)/(5sina-cosa)
=(3tana+2)/(5tana-1)
=8/9
sina•cosa
=(1/2)sin(2a)
=tana/(tan^2a+1)
=2/5
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