Volumes Q (2 Viewers)

[shaon0]

Consider the region bounded by y=3-x^2, y=x+x^2 and x=-1. The point P iis the intersection of y=3-x^2 and y=x+x^2 in the 1st quadrant.
i) Sketch the region. DONE
ii) Find the point P. DONE
iii) Hence, find the volume of the solid generated when this regiom is rotated about y=3.

I don't know how to approach part iii). Any help will be appreciated. Thanks

 

[GUSSSSSSSSSSSSS]

use slices perpendicular to x axis
cross sections will be annulus with outer radius equal to 3 - (x + x^2)
and inner radius equal to 3 - (3 - x^2)
integrate between 1 and -1


btw the answer i got was 1 is that right ???

 

[GUSSSSSSSSSSSSS]

i believe u are incorrect i got 0

*slits wrists*

 

[MC Squidge]

i havent done volumes yet, i cant work it out. so im gonna presume dd24 is right

 

[GUSSSSSSSSSSSSS]

i havent done volumes yet, i cant work it out. so im gonna presume dd24 is right

lol no physical object can have a volume of 0 =P

 

[gurmies]

Lol @ volume = 0. I haven't done this topic, but I assume that's wrong. Tsk tsk - failure to run a dimensional analysis.

 

[GUSSSSSSSSSSSSS]

dammit my latex thingy isnt working =[[[

Lol @ volume = 0. I haven't done this topic, but I assume that's wrong. Tsk tsk - failure to run a dimensional analysis.

you assume correct sire




and i still stand by my first answer of 1 as i just did it a second time
..........but then again i might be doin something fundamentally wrong xD

 

[Timothy.Siu]

u shud use shells its much easier than slices for this one

 

[GUSSSSSSSSSSSSS]

u shud use shells its much easier than slices for this one

YOU SURE ?!?!?!?

with slices it takes maybe 7 lines maximum =S
with shells ur gonna have 2 different regions =S

 

[gurmies]

I WANT TO DO VOLUMES ALREADY SO I CAN CONTRIBUTE - That is all.

 

[GUSSSSSSSSSSSSS]

I WANT TO DO VOLUMES ALREADY SO I CAN CONTRIBUTE - That is all.

lol teach urself gurmies...if i was able to...im sure you can too...ur better than me xD

 

[gurmies]

lol teach urself gurmies...if i was able to...im sure you can too...ur better than me xD

Def not better than you. I will probably learn it when I finish doing this other crap (i.e. the rest of my subjects -.-)

 

[study-freak]

 

[GUSSSSSSSSSSSSS]

lol fuck i just saw a mistake in the same place in my solutions (fucken evaluating integrals)

but ive just come up with a different answer to yours again now =S

i'll try post up my solution xD

 

[shaon0]

Thanks for the help.

 

[GUSSSSSSSSSSSSS]

gah fuck too tired ur answer was rite study freak

for me soooooooooooo many misreadings of my writing =[[[[[[[[[[[[[[[[

 

[study-freak]

gah fuck too tired ur answer was rite study freak

for me soooooooooooo many misreadings of my writing =[[[[[[[[[[[[[[[[

well, this question required too much simple algebra (simple, but easy to make mistakes)
I made those mistakes more than once in my 4u half yearlies lol...

 

[study-freak]

Thanks for the help.

no worries

 

[Drongoski]

no worries

Good work.

Saw the question about 23 mins ago and didn't see yr soln; Yr answer is same as mine.

 

[kwabon]

could someone please show or tell what exactly is the region you are rotating about y=3, because i am still struggling to figure what exactly is the region.

sorry for the inconvenience