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• bonkysleuth

  10 Sep 09, 10:50

  A circular cylinder , open at 1 end, has radius r cm and external surface area 27pi cm^2.

  Show that the volume of the cylinder V cm3 is given by V = pi/2 (27r - r^3)

  Given that r can vary, find the stationary value of V (I got 84.8cm, answer given is 84.4 cm)

  Would someone please confirm the accuracy for me. Thanks

   

  ***By the way, are real numbers referring to any numbers?***

• OHSheet

  10 Sep 09, 12:03

  alright. ill attach my soln.

  

  
  yes. you are right btw.

  The soln in the book might have used pi=3.14, while you might have used the pi value of 3.141592654(found in your calculator).

   

   

• wee_ws

  10 Sep 09, 14:39

  Hi,

    Thanks to OHSheet for his solution. It's fine to leave the answer in exact form, and we'll not have to worry about accuracy :) Thanks!

  Cheers,
  Wen Shih

• SBS n SMRT

  10 Sep 09, 14:42

  about leaving in exact form, let us follow O level instructions

  • Candidates are reminded not to leave their answer in pi unless otherwise stated, the calculator value of pi or 3.142 should be used
  • FOr answer that is not exact, leave to 3 sf

• wee_ws

  10 Sep 09, 18:18

  Hi,

    Thanks for pointing out, for I am not familiar with O-level instructions.

    I have checked that A-level H2 maths does not have the point in bullet 1.

    Thanks again!

  Cheers,
  Wen Shih

• SBS n SMRT

  10 Sep 09, 23:05

  welcome.........

• SBS n SMRT

  10 Sep 09, 23:06

  exception is where special angles are being used, for example,2 pi = 360 degrees in deg and 6.28 rad, pi can be used, but decimal will be preferred