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May 26, 2015

Posted by **Sara** on Friday, April 15, 2011 at 2:32am.

- calculus -
**Jai**, Friday, April 15, 2011 at 2:45amyes :)

do you want me to cite an example?

- calculus -
**E.T**, Friday, April 15, 2011 at 8:39amplease i need an example !

- calculus -
**Anonymous**, Friday, April 15, 2011 at 8:46amplease can you give me an example?

- calculus -
**Sara**, Friday, April 15, 2011 at 8:52amplease can you give me an example?

- calculus -
**Jai**, Friday, April 15, 2011 at 9:49amsorry i haven't replied to your reply earlier. anyway, here's an example:

there are many possible examples for this. but since we need to calculate volume (V) and surface area (SA), we choose a figure where its V and SA can easily/readily be calculated.

for instance we want to generate a shape of a cylinder,, note that this only requires a line parallel to x-axis (but not passing through x-axis) so that if it's revolved about the x-axis, it becomes a cylinder, or y = c, where c = any real number except zero. now we only need to find the bounds. for simplicity, let's choose one of the bounds as the origin.

recall that the V and SA of a cylinder is given by

V = π(r^2)*h

SA = 2πrh + 2πr^2

where r is radius and h = height

then we choose a value for V and SA . let's choose, for instance, 100 :

V = 100 = π(r^2)*h

SA = 100 = 2πrh + 2πr^2

since there are two equations, two unknowns, by substitution, we get two pairs of answers:

(i) r = 2.218 ; h = 20.327

(ii) r = 5.696 ; h = 3.08219

here, let's just choose (i).

when the equation y = c is revolved, the cylinder generated has a symmetry on x-axis (like it's lying/rolling on the floor). thus the radius is the y-coordinate and height is the x-coordinate. therefore y = c becomes

y = r = 2.218

with bounds from origin (0,0) to its height (20.327, 0)

hope this helps~ :)

- calculus -
**Sara**, Friday, April 15, 2011 at 10:15amthank you alot for your help I was really worried because i have to submit the answer tomorrow and i could not do any thing without your help

thank you again

- calculus -
**Jai**, Friday, April 15, 2011 at 11:13amyou're welcome~ :)

by the way, i just want to make a correction. fro the value of V and SA, it's not 100, it should be 100*pi = 314.16 . sorry i forgot the pi, because i cancelled it right away, but the answers for r and h is still the same. i'll just retype the correction:

...then we choose a value for V and SA . let's choose, for instance, 100*pi :

V = 100*pi = π(r^2)*h

SA = 100*pi = 2πrh + 2πr^2

...and the rest are correct.

so, the value of V and SA for the dimensions (i) and (ii) we got is equal to 100*pi or 314.16, not 100. sorry~ :P

- calculus -
**SQU**, Friday, April 15, 2011 at 1:41pmthenk you jai and sara

in which section you are sara?

- calculus -
**Sara**, Sunday, April 17, 2011 at 5:07amsectin 20 what about you?

- calculus -
**SQU**, Thursday, April 21, 2011 at 4:39amsection 70

nice to meet you

if you need any help just tell me

from wich college you are?