※ 引述《hank26592847 (无名氏)》之铭言：
: -积分sin/cos^3 dx
: 如果用sin变量变换答案会是-1/2*sec^2+c
: 但如果先把题目变-积分tan*sec^2 dx 再用变量变换sec^2答案会变成是-1/2*tan^2+c
: 请求各位大大帮小弟解惑 感谢
[sec(x)]^2 = 1 + [tan(x)]^2
(-1/2)[sec(c)]^2 + c
= [(-1/2) + c] - (1/2)[tan(x)]^2
= - (1/2)[tan(x)]^2 + c'