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[SOLVED] Find volume when curve rotated about y-axis

DeusAbscondus

Active member
Jun 30, 2012
176
Hi folks, could someone please take a look at this for me:

Here are the givens:

$$\text{ Find the volume when this curve is rotated about the y-axis }$$
$$y=-4lnx\ \text{ where } 0\le y \le 2$$

I have set my working out in a geogebra file, taken a screenshot and attached same below.

Would someone kindly take a look at my calculations and point out where I am going astray?

Really appreciate your time,
Deus Abs
 

tkhunny

Well-known member
MHB Math Helper
Jan 27, 2012
267
[tex]e^{0}\ne 0[/tex]

Good work otherwise.
 
Last edited:

DeusAbscondus

Active member
Jun 30, 2012
176
[tex]e^{0}\ne 0[/tex]

Good work otherwise.
Thank you kindly!

so: $$-2.2114547+2\pi \approx 3.97$$

Which is the solution given!

Do you know I kept making that error over and over again, through a frustrating hour or so; this makes me *sure* that I must find a different approach (different mind-set/attitude, perhaps) my checking procedure: cultivate an attitude of radical skepticism: something like: "question *everything* again regarding your working assumptions!"

Regs,
D'Abs
 

tkhunny

Well-known member
MHB Math Helper
Jan 27, 2012
267
Contrary to the too broad definition of privacy, another pair of eyes often is quite beneficial. :)
 

MarkFL

Administrator
Staff member
Feb 24, 2012
13,775
Very true! Oftentimes when I make an error like that, I will keep blindly making it over and over, and the best thing for me is to move on to something else, and when I come back to it after a break, then I am much more likely to catch the error. If I don't, then I will seek another pair of eyes! ;)