white_o
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So I did pi*r2*h for the volume of the cylinder which is 4x2*pi*9x

Then I did that = the volume of the spehere:
4x2*pi*9x = 4/3*4x2*pi

Then

(4/3*4x2*pi) / (4x2*pi) = 9x

1/34x2*pi = 9x

(1/34x2*pi)/9 = x

Right or wrong? Please help! Thanks
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TenOfThem
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(Original post by Qaiys)

So I did pi*r2*h for the volume of the cylinder which is 4x2*pi*9x

Then I did that = the volume of the spehere:
4x2*pi*9x = 4/3*4x2*pi

Then

(4/3*4x2*pi) / (4x2*pi) = 9x

1/34x2*pi = 9x

(1/34x2*pi)/9 = x

Right or wrong? Please help! Thanks
You do not have the correct formula for the volume of a sphere and you seem to have ignored the r

\dfrac{4}{3}\pi r^3


Then, I have to say - your algebraic manipulation is very wrong
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white_o
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(Original post by TenOfThem)
You do not have the correct formula for the volume of a sphere and you seem to have ignored the r

\dfrac{4}{3}\pi r^3


Then, I have to say - your algebraic manipulation is very wrong
So would 4x2*pi*9x = 4/3*8x3*pi be right?
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TenOfThem
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(Original post by Qaiys)
So would 4x2*pi*9x = 4/3*8x3*pi be right?
No

Why do you have no r in your work
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white_o
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(Original post by TenOfThem)
No

Why do you have no r in your work
The radius is 2x
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TenOfThem
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(Original post by Qaiys)
The radius is 2x
The radius of the cylinder is 2x

Not the radius of the sphere
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white_o
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(Original post by TenOfThem)
The radius of the cylinder is 2x

Not the radius of the sphere
So how do I find the radius of the sphere?
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TenOfThem
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(Original post by Qaiys)
So how do I find the radius of the sphere?
It tells you in the question that it is r
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white_o
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(Original post by TenOfThem)
It tells you in the question that it is r
ohhh, oh yeah. Okay so

pi*r^2h = pi*4x^2*9x

pi*4x^2*9x = 4/3pi*r"3

Then rearrange for x?
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TenOfThem
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(Original post by Qaiys)
ohhh, oh yeah. Okay so

pi*r^2h = pi*4x^2*9x

pi*4x^2*9x = 4/3pi*r"3

Then rearrange for x?
well rearrange for r, since the question asks for r in terms of x

but yes
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white_o
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(Original post by TenOfThem)
well rearrange for r, since the question asks for r in terms of x

but yes
Oh yeah sorry >.< and thanks! I'll try and post in a sec
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TenOfThem
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(Original post by Qaiys)
Oh yeah sorry >.< and thanks! I'll try and post in a sec


Perseverance is the first stage on the route to success
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white_o
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4x^2*pi*9x = 4/3*pi*r^3

(4x^2*pi*9x)/(4/3*pi) = r^3

cube root((4x^2*pi*9x)/(4/3*pi)=r

Would the pi's cancel out?

Thanks
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white_o
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(Original post by TenOfThem)


Perseverance is the first stage on the route to success
Haha absolutely :P Thanks!
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TenOfThem
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(Original post by Qaiys)
4x^2*pi*9x = 4/3*pi*r^3

(4x^2*pi*9x)/(4/3*pi) = r^3

cube root((4x^2*pi*9x)/(4/3*pi)=r

Would the pi's cancel out?

Thanks

The pi does cancel
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white_o
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(Original post by TenOfThem)
The pi does cancel
So would cube root((4x^2*9x)/(4/3)) = r be the final answer?
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TenOfThem
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(Original post by Qaiys)
So would cube root((4x^2*9x)/(4/3)) = r be the final answer?
You need to work on your algebra skills

Firstly 4x^2 * 9x = 36x^3

Then dividing by \frac{4}{3} is the same as multiplying by \frac{3}{4}
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white_o
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(Original post by TenOfThem)
You need to work on your algebra skills

Firstly 4x^2 * 9x = 36x^3

Then dividing by \frac{4}{3} is the same as multiplying by \frac{3}{4}
Gahh, I'm not usually this terrible I promise, I've been revising allll day for my exam tomorrow


So 36x^3 * 4/3 = 108x*3/4 = 27x^3

so r = 3x?
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TenOfThem
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(Original post by Qaiys)
Gahh, I'm not usually this terrible I promise, I've been revising allll day for my exam tomorrow


So 36x^3 * 4/3 = 108x*3/4 = 27x^3

so r = 3x?
woo hooooooo

Yes
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white_o
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(Original post by TenOfThem)
woo hooooooo

Yes
Haha sorry for being so rubbish!! Thanks a lot
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