xiao2222xiao
幼苗
共回答了18个问题采纳率:100% 举报
要tan(A-B)=sin2B/(5-cos2B),
只要(tanA-tanB)/(1+tanAtanB)=[2tanB/(1+tan^B)]/[5-(1-tan^B)/(1+tan^B)],其中tan^B=(tanB)^2,
化简右边得(tanA-tanB)/(1+tanAtanB)=2tanB/(4+6tan^B),
去分母得(tanA-tanB)(2+3tan^B)=tanB(1+tanAtanB),
整理得tanA(2+2tan^B)=tanB(3+3tan^B),
1+tan^B>0,
∴只需2tanA=3tanB.
1年前
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