# Math Help - Shell method (volume)

1. ## Shell method (volume)

i m having problems using the shell method.. basically the formula i have is integral (2 pie) (radius) (height). using this formula i have y = 2x, y = x/2, x =1, flip this about the y axis.

how do i know which one is the height, how do i know which one is radius, if someone can help me understand this it would be greatly appreciated. answer is 1pie btw.

2. Volume by cylindrical shell about the y-axis

$V=\int_a^b 2 \pi x f(x) dx
$

x=radius (the radius in this case would just be x)
f(x)= height
a and b are the bounds

in this case your height would be the top function-bottom function which is 2x-(x/2) and the bounds looks like it would 0 to 1.

Hope this helps