MHB NICK's question at Yahoo Answers regarding a solid of revolution

  • Thread starter Thread starter MarkFL
  • Start date Start date
  • Tags Tags
    Revolution Solid
MarkFL
Gold Member
MHB
Messages
13,284
Reaction score
12
Here is the question:

Calculus ii question!?

Using disks or washers, find the volume of the solid obtained by rotating the region bounded by the curves y=x, y=0, x=2, and x=4 about the line x=1.

Volume = ?

Here is a link to the question:

Calculus ii question!? - Yahoo! Answers

I have posted a link there to this topic so the OP can find my response.
 
Mathematics news on Phys.org
Hello NICK,

Using washers, we find that we have one interval where the inner radius is a function of $y$, and another in which the inner radius is constant. For both intervals, the outer radius is constant.

Thus, we find the volume is:

$$V=\pi\left(\int_0^2 3^2-1^2\,dy+\int_2^4 3^2-(y-1)^2\,dy \right)=$$

$$\pi\left(\left[8y \right]_0^2+\left[9y-\frac{1}{3}(y-1)^3 \right]_2^4 \right)=\pi\left(16+27-\frac{53}{3} \right)=\frac{76\pi}{3}$$

To check our work, let's use the shell method:

$$V=2\pi\int_2^4(x-1)x\,dx=2\pi\left[\frac{x^3}{3}-\frac{x^2}{2} \right]_2^4=$$

$$2\pi\left(\frac{40}{3}-\frac{2}{3} \right)=\frac{76\pi}{3}$$
 
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. In Dirac’s Principles of Quantum Mechanics published in 1930 he introduced a “convenient notation” he referred to as a “delta function” which he treated as a continuum analog to the discrete Kronecker delta. The Kronecker delta is simply the indexed components of the identity operator in matrix algebra Source: https://www.physicsforums.com/insights/what-exactly-is-diracs-delta-function/ by...
Fermat's Last Theorem has long been one of the most famous mathematical problems, and is now one of the most famous theorems. It simply states that the equation $$ a^n+b^n=c^n $$ has no solutions with positive integers if ##n>2.## It was named after Pierre de Fermat (1607-1665). The problem itself stems from the book Arithmetica by Diophantus of Alexandria. It gained popularity because Fermat noted in his copy "Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos, et...
I'm interested to know whether the equation $$1 = 2 - \frac{1}{2 - \frac{1}{2 - \cdots}}$$ is true or not. It can be shown easily that if the continued fraction converges, it cannot converge to anything else than 1. It seems that if the continued fraction converges, the convergence is very slow. The apparent slowness of the convergence makes it difficult to estimate the presence of true convergence numerically. At the moment I don't know whether this converges or not.
Back
Top