※ 引述《hero010188 (咖啡乾了啦)》之銘言：
: https://i.imgur.com/X3fobVl.jpg
另解
theta = k
LHS = [tan(k) - sec(k) + 1]/[sec(k) - tan(k) + 1]
= [tank(seck + 1) - tanktank]/[(seck + 1)^2 - tank(seck + 1)]
= {(tank)[seck + 1 - tank]}/{[seck + 1][seck + 1 - tank]}
= [tank]/[seck + 1]
= [sink]/[1 + cosk]
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