I was solving an example problem using a different method using a formula linked below. The answer I ended up has an "x" in the denominator which isn't there in solution the book presents. I've failed to figure out where I made a mistake. Could you please help me? Thanks a lot.
The algebraic expression under the integral in line 7 should reduce to just 2y. The integral of that is y^2, which simplifies the remaining lines to the correct answer.