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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Specialist Mathematics => Topic started by: madoscar65 on May 31, 2011, 04:21:34 pm

Title: Volume Of Revolution
Post by: madoscar65 on May 31, 2011, 04:21:34 pm

Hi people,
I've been trying to solve this problem in Essential Specialist Maths Exercise 8D question 13 but I just can't get the right answer.

The question is: Find the volume of the solid generated when the region enclosed by y =√(3x + 1), y =√(3x), y = 0 and   x = 1 is rotated about the x axis.

I used V=pi * integral from -1/3 to 1 (√(3x+1))^2-(√3x)^2)dx and I get 4pi/3
Answer is 7pi/6
So hope you guys can help out :)

Thanks

Title: Re: Volume Of Revolution
Post by: moekamo on May 31, 2011, 04:33:11 pm

dont do the whole integral from -1/3 to 1. Only the sqrt(3x+1) should be done with those terminals, the sqrt(3x) is from 0 to 1(its not defined for anything less than 0). this should get 7pi/6

Title: Re: Volume Of Revolution
Post by: recovered on June 01, 2011, 08:42:31 pm

V= pi*(integral from -1/3 to 1 of 3x+1(as it is y^2) - integral from 0 to 1 of 3x (again y^2)

this shld defs get u the right answer
if u r using shortcuts of some kind, maybe avoid them
hope it helps