Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1992
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1992

[Date Index] [Thread Index] [Author Index]

Search the Archive

A negative volume!

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: A negative volume!
  • From: "Roger B. Kirchner" <kirchner at cs.umn.edu>
  • Date: Tue, 10 Mar 92 10:55:22 -0600

Let V be the volume of the solid inside the first octant of the unit
sphere and outside the cylinder with cylindrical equation r = Sin[t].
Computing in cylindrical coordinates, 

In[1]:= Integrate[r, {z, 0, (1 - r^2)^(1/2)}]

                    2
Out[1]= r Sqrt[1 - r ]

In[2]:= Integrate[%, {r, Sin[t], 1}]

              2            2
        Cos[t]  Sqrt[Cos[t] ]
Out[2]= ---------------------
                  3

In[3]:= Integrate[%, {t, 0, Pi/2}]

          2
Out[3]= -(-)
          9

Thus V = -2/9!

Anybody have any suggestions on how to avoid this kind of problem?
Roger Kirchner





  • Prev by Date: finding roots of user defn. functions
  • Next by Date: Third Annual Conference on College Mathematics
  • Previous by thread: finding roots of user defn. functions
  • Next by thread: Re: A negative volume!