Here's the question you clicked on:
patbatE21
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
|dw:1324412465826:dw|
something similar to this right?
then we can integrate, or sum up the areas of circles, generated by the function from 3 to 9 i believe
May I please see a full work out please?
\[\sum_{3}^{4}\pi[f(x)]^2\ \Delta x\] \[\pi \int_{3}^{9}(\frac{9}{x})^2dx\]
|dw:1324412686951:dw|
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
are you still stuck? can you not integrate\[\pi\int_{3}^{9}\frac{9^2}{x^2}dx\]? or are you having another problem?
http://www.wolframalpha.com/input/?i=integrate+pi*%289%2Fx%29%5E2+from+3+to+9 18pi looks good to me