fsa102sina
幼苗
共回答了26个问题采纳率:92.3% 举报
tan(π/4+α)=1/2
∴ [tan(π/4)+tanα]/[1-tan(π/4)tanα]=1/2
∴ (1+tanα)/(1-tanα)=1/2
∴ 2+2tanα=1-tanα
∴ tanα=-1/3
∴ tan2α=2tanα/(1-tan²α)=2*(-1/3)/[1-(-1/3)²]=(-2/3)/(8/9)=-3/4
1年前
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求sin2阿~-cos方阿~除以1+cos2阿的值
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sin2阿~-cos方阿~除以1+cos2阿 =(sin²α-cos²α)/(2cos²α+sin²α) 分子分母同时除以cos²α =(tan²α-1)/(2+tan²α) =(-8/9)/(19/9( =-8/19