The curve is $y=\frac{1}{1+x^2}$, on the interval [1, 4] and the line is x = -1.
The integral I have set up using the cylindrical shell method is $$ 2\pi \int_1^4 \frac{x+1}{1+x^2}\, dx $$
but I'm not sure if it is correct. I'm confused about whether I should subtract the line from the x value or the x value from the line to get the radius since the results are different.