赞 qiying1207 花朵
共回答了20个问题采纳率：90% 举报
(1-sina)/cosa=(sin²a/2+cos²a/2-2sina/2cosa/2)/(cos²a/2-sin²a/2)
=(tan²a/2+1-2tana/2)/(1-tan²a/2)
=(tana/2-1)²/(1-tan²a/2)
=(1-tana/2)/(1+tana/2)
=(tanπ/4-tana/2)/(1+tanπ/4·tana/2)
=tan(π/4-a/2)
=(tan²a/2+1-2tana/2)/(1-tan²a/2)
=(tana/2-1)²/(1-tan²a/2)
=(1-tana/2)/(1+tana/2)
=(tanπ/4-tana/2)/(1+tanπ/4·tana/2)
=tan(π/4-a/2)
1年前
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