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的确不对：
cosa/(1-sina)=(cos^2(a/2)-sin^2(a/2))/(cos^2(a/2)-2sin(a/2)cos(a/2)+sin^2(a/2)))
=(cos(a/2)+sin(a/2))(cos(a/2)-sin(a/2))/(cos(a/2)-sin(a/2))^2
=(cos(a/2)+sin(a/2))/(cos(a/2)-sin(a/2))=(1+tan(a/2))/(1-tan(a/2))=2/(π-2)
故：tan(a/2)=(4-π)/π
1年前
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