Gabriel's horn problem

polarus

New member
Joined
Dec 1, 2014
Messages
3
Gabriel’s Horn All parts of this problem are based on the function f(x) = 1/x^2/3.


(1) Find an expression for the area between f(x) and the x-axis for x = 1 to x = for some constant > 1.
(2) Take the limit as --> of your answer to (1) to find the area under the curve f(x) for x-values from 1 to .
(3) Find the volume of the solid formed by rotating the region bounded by f(x) and the x-axis around the x-axis for x-values 1 x , for some constant > 1.
(4) Take the limit as ☹ --> of your answer to (3) to find the volume of this infinitely long “trumpet” (known as Gabriel’s Horn).
(5) How can your results to (2) and (4) both be true? Explain.

I solved to following as below, my question is how did I end up with a negative volume for #4?

112fzav.jpg



 
You have a sign wrong in (3)
\(\displaystyle \int \pi\space (x^{-\frac{2}{3}})^2\space =\space \pi\space \int x^{-\frac{4}{3}}\space =\space -3\space \pi\space x^{-\frac{1}{3}}\)
 
Top