※ 引述《hank26592847 (無名氏)》之銘言：
: -積分sin/cos^3 dx
: 如果用sin變數變換答案會是-1/2*sec^2+c
: 但如果先把題目變-積分tan*sec^2 dx 再用變數變換sec^2答案會變成是-1/2*tan^2+c
: 請求各位大大幫小弟解惑 感謝
[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'