想問一條M2 indefinite integrals

http://img98.imageshack.us/img98/4757/51469091.png

圖片參考：http://img98.imageshack.us/img98/4757/51469091.png


2011-01-30 16:04:18 補充：
There is a mistake in the calculation, the step to transform x to u should be
I=∫4(cos u/sin^2 u)(cos u du/2) = 2∫ cot^u du
All subsequent steps should be mutiplied by 4
and the answer = -sqrt(1-4x^2)/x - arc sin 2x +c

2011-01-30 16:09:46 補充：
Please see the updated solution:
http://img171.imageshack.us/img171/8379/28967917.png

thx a lot !!! ^^