Volume of a cylinder and sphere?Watch

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Thread starter 5 years ago
#1 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 0
5 years ago
#2
(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 Then, I have to say - your algebraic manipulation is very wrong
0
Thread starter 5 years ago
#3
(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 Then, I have to say - your algebraic manipulation is very wrong
So would 4x2*pi*9x = 4/3*8x3*pi be right?
0
5 years ago
#4
(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
0
Thread starter 5 years ago
#5
(Original post by TenOfThem)
No

Why do you have no r in your work
The radius is 2x
0
5 years ago
#6
(Original post by Qaiys)
The radius is 2x
The radius of the cylinder is 2x

Not the radius of the sphere
0
Thread starter 5 years ago
#7
(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?
0
5 years ago
#8
(Original post by Qaiys)
So how do I find the radius of the sphere?
It tells you in the question that it is r
0
Thread starter 5 years ago
#9
(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?
0
5 years ago
#10
(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
0
Thread starter 5 years ago
#11
(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 0
5 years ago
#12
(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
0
Thread starter 5 years ago
#13
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
0
Thread starter 5 years ago
#14
(Original post by TenOfThem) Perseverance is the first stage on the route to success
Haha absolutely :P Thanks!
0
5 years ago
#15
(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
0
Thread starter 5 years ago
#16
(Original post by TenOfThem)
The pi does cancel
So would cube root((4x^2*9x)/(4/3)) = r be the final answer?
0
5 years ago
#17
(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 Then dividing by is the same as multiplying by 0
Thread starter 5 years ago
#18
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?
0
5 years ago
#19
(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
0
Thread starter 5 years ago
#20
(Original post by TenOfThem)
woo hooooooo Yes
Haha sorry for being so rubbish!! Thanks a lot 0
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