The region bounded by the line y = 1 and the parabola x^2 = 4y

is revolved about the line y = 1.....

Take the rectangular elements of area parallel to the axis of revolution

I set :

radius = 1 - y

height = $\displaystyle 2\sqrt{y} - (-2\sqrt{y})$

$\displaystyle 2\pi \int_{-2}^{2} (2\sqrt{y} - (-2\sqrt{y})(1 - y)dy$

$\displaystyle 2\pi \int_{-2}^{2} (4\sqrt{y})(1 - y)dy$

i need help

my answer seems to be undefined...