I would be grateful if someone would have a look at the working on this link.I cant paste picture here or save in correct format and upload..

http://www.wolframalpha.com/input/po...&s=41&button=1

could someone please talk me thru this problem???

I understand to use u and du but am unsure where the values 1/2 and the number 2 in 2u come from.In my book it says to use a compensatory value.Im guessin here that 2 compensates 1/2 or is it the other way round? I will be using arctan rather than tan^-1.Any help will be great.Thanks