prove cos2A=(1-tan^2)/(1+tan^2A)?
回答 (2)
2016-09-25 5:07 pm
2016-09-25 5:05 pm
RHS = (1 - tan^2A)/sec^2A =
cos^2A(1 - tan^2A) =
cos^2A - sin^2A =
cos(2A) = LHS
cos^2A(1 - tan^2A) =
cos^2A - sin^2A =
cos(2A) = LHS
收錄日期: 2021-04-21 23:27:01
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https://hk.answers.yahoo.com/question/index?qid=20160925085742AA02Oaq