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sina=2/3,cos(x-2a)等于多少?
人气:461 ℃ 时间:2020-07-16 09:25:30
解答
解cos(π-2a)
=-cos2a
=-[1-2sin^2a]
=2sin^2a-1
=2[2/3]^2-1
=8/9-1
=-1/9.
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