# Thread: More volume of graphs

1. ## More volume of graphs

from the graph 2x + y = 2, a solid is generated by revolving it about the x-axis. here is the graph with the endpoints

For my answer, i got pi/3 is that correct?

2. That's not what I got. Can you show us how you set up the integral?

3. Originally Posted by drumist
That's not what I got. Can you show us how you set up the integral?
i set up my integral in terns of x

i dont know how to use the integral sign here, so excuse me as i try to explain it.

the integral pi/3 times the integral of -2x+2 dx from 2 to 1 [i have a feeling thats wrong]

4. Originally Posted by >_<SHY_GUY>_<
from the graph 2x + y = 2, a solid is generated by revolving it about the x-axis. here is the graph with the endpoints

For my answer, i got pi/3 is that correct?
Just use the method of disks

$V = \pi\int_0^1(-2x + 2)^2 dx$
$V = \pi\int_0^1(4x^2 - 8x + 4)dx$
$V = \pi\left[\frac{4x^3}{3} - 4x^2 + 4x\right]_0^1$
$V = \frac{4\pi}{3}$

5. Originally Posted by eddie2042
Just use the method of disks

$V = \pi\int_0^1(-2x + 2)^2 dx$
$V = \pi\int_0^1(4x^2 - 8x + 4)dx$
$V = \pi\left[\frac{4x^3}{3} - 4x^2 + 4x\right]_0^1$
$V = \frac{4\pi}{3}$
how do you know when to use disk? how is the way i approached the problem wrong? Im just really curious as to how to determine it

thank you so much