夜空下的狼
幼苗
共回答了32个问题采纳率：87.5% 举报
(1-sinx)/cosx
=[sin²(x/2)+cos²(x/2)-2sin(x/2)cos(x/2)]/[cos²(x/2)-sin²(x/2)]
=[cos(x/2)-sin(x/2)]²/{[cos(x/2)+sin(x/2)]*[cos(x/2)-sin(x/2)]}
=[cos(x/2)-sin(x/2)]/[cos(x/2)+sin(x/2)]
分子分母同时除以cos(x/2)
=[1-tan(x/2)]/[1+tan(x/2)]
1年前
6
