# Math Help - Disk method.

1. ## Disk method.

find the volume of the solid generated by revolving each region about the y-axis

the region in the first quadrant bounded above by the parabola y=x^2, below by the x, axis, and on the right by the line x=2.

Worked this problem out like 5 times idk why i cant get the right answer. cannot find what im doing wrong. It seems pretty simple. Answers 8Pi. HELP PLZ

2. Originally Posted by jeffjohnson
find the volume of the solid generated by revolving each region about the y-axis

the region in the first quadrant bounded above by the parabola y=x^2, below by the x, axis, and on the right by the line x=2.

Worked this problem out like 5 times idk why i cant get the right answer. cannot find what im doing wrong. It seems pretty simple. Answers 8Pi. HELP PLZ
washers ...

$R = 2$

$r = \sqrt{y}$

$V = \pi \int_0^4 2^2 - (\sqrt{y})^2 \, dy
$

work it out ...

3. Originally Posted by jeffjohnson
find the volume of the solid generated by revolving each region about the y-axis

the region in the first quadrant bounded above by the parabola y=x^2, below by the x, axis, and on the right by the line x=2.

Worked this problem out like 5 times idk why i cant get the right answer. cannot find what im doing wrong. It seems pretty simple. Answers 8Pi. HELP PLZ
Hi jeff,

using the integral of cylindrical surface areas,

$\int_{0}^22{\pi}\left((x)x^2\right)dx=2{\pi}\left( \frac{2^4}{4}\right)=\frac{2^5{\pi}}{4}$