I tried to understand the solution to this problem but one thing I don't get:

the problem states: find the volume of the solid obtained by rotating the region bounded by the curves y= 1 + sec(x), y = 3, about y = 1;

so, the inner radius is (1 + sec(x)) - 1 = sex(x); the outer radius is 3-1 = 2; and we have the area A(x) = pi(4 - sec^2(x))

and it is integrated from -pi/3 to pi/3; how does they get these x-axis coordinates of pi/3?

thank you