I'm currently working this problem

https://webwork.math.lsu.edu/webwork...d407a3c4c1.png

pretty unsuccessfully. I tried to use the derivative of arctan and the general power rule and as a result I got: https://webwork.math.lsu.edu/webwork...cb2ccf7b71.png

But this is wrong. Any thoughts? Thanks to anybody that helps. :D