题目

已知tan(π/4+α)=1/5,求(sin2α-sin²α)/(1-cos2α)的值
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提问时间：2020-12-06

答案

由已知可得 tanα=tan[(α+π/4)-π/4]=[tan(α+π/4)-tan(π/4)] / [1+tan(α+π/4)tan(π/4)]=(1/5-1)/(1+1/5)= -2/3 ,所以 [sin(2α)-(sinα)^2] / [1-cos(2α)] =sinα(2cosα-sinα) / [2(sinα)^2]=(2cosα-si...