If csc(x) 16/13 in quad 1, find cos(2x)?
回答 (2)
2016-07-14 12:37 am
maybe
2016-07-14 12:24 am
hint : the reference triangle is { √87 , 13 , 16 }
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https://hk.answers.yahoo.com/question/index?qid=20160713161606AANcnso