Hello.

I have been working with U-substitution the last two days, and things have been fine, until I got to a certain problem. I went about it the same way that I have done with all of my other problems, and yet the answer is wrong, and I dont understand why. Rather than try to code it out here, I took a picture from my workbook, and I hope that is ok.

Can someone explain to me why I cant substitute like I have? As far as I can see after looking over it several times, I have done things exactly as I always have. I have a gut feeling that it has to do with the fact that there is the 1 + sqrt X in the denominator, but I still dont see why it wouldnt work. Thanks!