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# Volume integration

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1. Prove that the volume of a solid generated by completely rotating the function y = 6 / (2x + 1)^1/2 around the x axis between x = 0 and x = 4 equals 36 pi ln3 units cubed

I get so far then I don't know where to go next this what I've got

y^2 = 36(2x + 1)^1/4

V = pi [72/5 (2x + 1)^5/4 ] between 4 and 0, 4 being at top of bracket don't know how to write that on here

So pi {[72/5(9)^5/4]-[72/5]}
2. Not sure how you've squared it. If then

as you have to use the multiplying power rule for the denomoinator square.
3. (Original post by NotNotBatman)
Not sure how you've squared it. If then

as you have to use the multiplying power rule for the denomoinator square.
oh thanks that makes more sense
4. (Original post by NotNotBatman)
Not sure how you've squared it. If then

as you have to use the multiplying power rule for the denomoinator square.
ive done what youve said and when ive integrated and subbed the x's in I get...

V= pi {[24(9)^3/4]-[24]}
5. (Original post by Custardcream000)
ive done what youve said and when ive integrated and subbed the x's in I get...

V= pi {[24(9)^3/4]-[24]}
There's a problem with how you've integrated. Remember

What did you get as your integral?
6. (Original post by NotNotBatman)
There's a problem with how you've integrated. Remember

What did you get as your integral?
oh duh yeah i brought it up thats why
7. (Original post by Custardcream000)
oh duh yeah i brought it up thats why
so you get....

v= pi {[18ln(9)^1/4]-[18 ln(1)]}
8. (Original post by NotNotBatman)
Not sure how you've squared it. If then

as you have to use the multiplying power rule for the denomoinator square.

One thing is wrong, the power.

I think you're doing 2 x 1/2 =1/4, but 2 x 1/2 = 1

So you've got the integration right except for the power of 1/4

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