Have you drawn a graph of this? The line y= x crosses the line x= 2 at, of course, (2, 2). But the region you are rotating around the line x= 1 goes down to y= 0. If you are using "disks or washers" you will have to do this in two parts: for y= 0 to 2, The outer radius is 4- 1= 3 and the inner radius is 2- 1= 1. For y from 2 to 4, the inner radius is y- 1 and the outer radius is 3.