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(2sinα+cosα)/(sinα-3cosα)=-5 求cos2α
人气:384 ℃ 时间:2020-06-03 01:07:48
解答
2sinα+cosα=-5sinα+15cosα
7sinα=14cosα
tanα=0.5
cos2α=((cosα)^2-(sinα)^2)/((cosα)^2+(sinα)^2)
=(1-(tanα)^2)/(1+(tanα)^2)
=3/5
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