## patbatE21 Group Title Find the volume generated by revolving about the x-axis the area bounded by xy = 9, the x-axis and lines x = 3 and x=9 2 years ago 2 years ago

1. amistre64 Group Title

|dw:1324412465826:dw|

2. amistre64 Group Title

something similar to this right?

3. patbatE21 Group Title

Yess

4. amistre64 Group Title

then we can integrate, or sum up the areas of circles, generated by the function from 3 to 9 i believe

5. patbatE21 Group Title

6. patbatE21 Group Title

@ amistre64 Alright

7. amistre64 Group Title

$\sum_{3}^{4}\pi[f(x)]^2\ \Delta x$ $\pi \int_{3}^{9}(\frac{9}{x})^2dx$

8. amistre64 Group Title

|dw:1324412686951:dw|

9. amistre64 Group Title

if we take any arbitrary circle created by spinning this about the x axis; we get an area of: pi (y)^2 pi (9/x)^2 the volume generated is then adding up all the circles made from x=3 to x=9

10. TuringTest Group Title

are you still stuck? can you not integrate$\pi\int_{3}^{9}\frac{9^2}{x^2}dx$? or are you having another problem?

11. patbatE21 Group Title

@ amistre64 Alright

12. patbatE21 Group Title

is it 18pi?

13. amistre64 Group Title

http://www.wolframalpha.com/input/?i=integrate+pi*%289%2Fx%29%5E2+from+3+to+9 18pi looks good to me