how to find the volume of intersection between eleptic cylinder and cylinder?
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let C be the eleptic cylinder C = {$frac{y^2}{4} + z^2leq 1$}.
let D be the cylinder {$x^2 + z^2 leq 1$}
find the volume of intersection of C and D
this is what i did :
$$V = int_{z=-1}^{z=1}int_{y=-sqrt{4-4z^2}}^{y=sqrt{4-4z^2}}int_{x=-sqrt{1-z^2}}^{x=sqrt{1-z^2}} 1{ dx}{ dy}{ dz} $$
$$= int_{z=-1}^{z=1}int_{y=-sqrt{4-4z^2}}^{y=sqrt{4-4z^2}}2sqrt{1-z^2}{ dy}{ dz}=$$
$$= int_{z=-1}^{z=1}2sqrt{1-z^2}*2sqrt{4-4z^2} { dz}= int_{z=-1}^{z=1}4sqrt{4z^4-8z^2+4} { dz}=int_{z=-1}^{z=1}4sqrt{(2z^2 -2)^2} { dz} = 10frac{2}{3}$$
why did i get negative volume ?
did i do it correctly ? or am i missing something
integration multivariable-calculus
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|
show 3 more comments
$begingroup$
let C be the eleptic cylinder C = {$frac{y^2}{4} + z^2leq 1$}.
let D be the cylinder {$x^2 + z^2 leq 1$}
find the volume of intersection of C and D
this is what i did :
$$V = int_{z=-1}^{z=1}int_{y=-sqrt{4-4z^2}}^{y=sqrt{4-4z^2}}int_{x=-sqrt{1-z^2}}^{x=sqrt{1-z^2}} 1{ dx}{ dy}{ dz} $$
$$= int_{z=-1}^{z=1}int_{y=-sqrt{4-4z^2}}^{y=sqrt{4-4z^2}}2sqrt{1-z^2}{ dy}{ dz}=$$
$$= int_{z=-1}^{z=1}2sqrt{1-z^2}*2sqrt{4-4z^2} { dz}= int_{z=-1}^{z=1}4sqrt{4z^4-8z^2+4} { dz}=int_{z=-1}^{z=1}4sqrt{(2z^2 -2)^2} { dz} = 10frac{2}{3}$$
why did i get negative volume ?
did i do it correctly ? or am i missing something
integration multivariable-calculus
$endgroup$
$begingroup$
correct edited *
$endgroup$
– Mather
Dec 15 '18 at 15:12
$begingroup$
The integral looks right to me, and you certainly shouldn't get a negative answer. Please post your calculations, so we can pinpoint the error.
$endgroup$
– saulspatz
Dec 15 '18 at 15:15
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i have posted extended calculation
$endgroup$
– Mather
Dec 15 '18 at 15:28
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I agree up to the very last equal sign. How did you do the last integral? I'm guessing you simplified $sqrt{z^2-1}$ as $z^2-1$ instead of $1-z^2$.
$endgroup$
– saulspatz
Dec 15 '18 at 15:31
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the squrt of $(2z - 2)^2 $ is $ 2z-2 $ so doing the integral it is $ z^3/3 - 2z $
$endgroup$
– Mather
Dec 15 '18 at 15:33
|
show 3 more comments
$begingroup$
let C be the eleptic cylinder C = {$frac{y^2}{4} + z^2leq 1$}.
let D be the cylinder {$x^2 + z^2 leq 1$}
find the volume of intersection of C and D
this is what i did :
$$V = int_{z=-1}^{z=1}int_{y=-sqrt{4-4z^2}}^{y=sqrt{4-4z^2}}int_{x=-sqrt{1-z^2}}^{x=sqrt{1-z^2}} 1{ dx}{ dy}{ dz} $$
$$= int_{z=-1}^{z=1}int_{y=-sqrt{4-4z^2}}^{y=sqrt{4-4z^2}}2sqrt{1-z^2}{ dy}{ dz}=$$
$$= int_{z=-1}^{z=1}2sqrt{1-z^2}*2sqrt{4-4z^2} { dz}= int_{z=-1}^{z=1}4sqrt{4z^4-8z^2+4} { dz}=int_{z=-1}^{z=1}4sqrt{(2z^2 -2)^2} { dz} = 10frac{2}{3}$$
why did i get negative volume ?
did i do it correctly ? or am i missing something
integration multivariable-calculus
$endgroup$
let C be the eleptic cylinder C = {$frac{y^2}{4} + z^2leq 1$}.
let D be the cylinder {$x^2 + z^2 leq 1$}
find the volume of intersection of C and D
this is what i did :
$$V = int_{z=-1}^{z=1}int_{y=-sqrt{4-4z^2}}^{y=sqrt{4-4z^2}}int_{x=-sqrt{1-z^2}}^{x=sqrt{1-z^2}} 1{ dx}{ dy}{ dz} $$
$$= int_{z=-1}^{z=1}int_{y=-sqrt{4-4z^2}}^{y=sqrt{4-4z^2}}2sqrt{1-z^2}{ dy}{ dz}=$$
$$= int_{z=-1}^{z=1}2sqrt{1-z^2}*2sqrt{4-4z^2} { dz}= int_{z=-1}^{z=1}4sqrt{4z^4-8z^2+4} { dz}=int_{z=-1}^{z=1}4sqrt{(2z^2 -2)^2} { dz} = 10frac{2}{3}$$
why did i get negative volume ?
did i do it correctly ? or am i missing something
integration multivariable-calculus
integration multivariable-calculus
edited Dec 15 '18 at 15:43
Mather
asked Dec 15 '18 at 15:07
Mather Mather
3317
3317
$begingroup$
correct edited *
$endgroup$
– Mather
Dec 15 '18 at 15:12
$begingroup$
The integral looks right to me, and you certainly shouldn't get a negative answer. Please post your calculations, so we can pinpoint the error.
$endgroup$
– saulspatz
Dec 15 '18 at 15:15
$begingroup$
i have posted extended calculation
$endgroup$
– Mather
Dec 15 '18 at 15:28
$begingroup$
I agree up to the very last equal sign. How did you do the last integral? I'm guessing you simplified $sqrt{z^2-1}$ as $z^2-1$ instead of $1-z^2$.
$endgroup$
– saulspatz
Dec 15 '18 at 15:31
$begingroup$
the squrt of $(2z - 2)^2 $ is $ 2z-2 $ so doing the integral it is $ z^3/3 - 2z $
$endgroup$
– Mather
Dec 15 '18 at 15:33
|
show 3 more comments
$begingroup$
correct edited *
$endgroup$
– Mather
Dec 15 '18 at 15:12
$begingroup$
The integral looks right to me, and you certainly shouldn't get a negative answer. Please post your calculations, so we can pinpoint the error.
$endgroup$
– saulspatz
Dec 15 '18 at 15:15
$begingroup$
i have posted extended calculation
$endgroup$
– Mather
Dec 15 '18 at 15:28
$begingroup$
I agree up to the very last equal sign. How did you do the last integral? I'm guessing you simplified $sqrt{z^2-1}$ as $z^2-1$ instead of $1-z^2$.
$endgroup$
– saulspatz
Dec 15 '18 at 15:31
$begingroup$
the squrt of $(2z - 2)^2 $ is $ 2z-2 $ so doing the integral it is $ z^3/3 - 2z $
$endgroup$
– Mather
Dec 15 '18 at 15:33
$begingroup$
correct edited *
$endgroup$
– Mather
Dec 15 '18 at 15:12
$begingroup$
correct edited *
$endgroup$
– Mather
Dec 15 '18 at 15:12
$begingroup$
The integral looks right to me, and you certainly shouldn't get a negative answer. Please post your calculations, so we can pinpoint the error.
$endgroup$
– saulspatz
Dec 15 '18 at 15:15
$begingroup$
The integral looks right to me, and you certainly shouldn't get a negative answer. Please post your calculations, so we can pinpoint the error.
$endgroup$
– saulspatz
Dec 15 '18 at 15:15
$begingroup$
i have posted extended calculation
$endgroup$
– Mather
Dec 15 '18 at 15:28
$begingroup$
i have posted extended calculation
$endgroup$
– Mather
Dec 15 '18 at 15:28
$begingroup$
I agree up to the very last equal sign. How did you do the last integral? I'm guessing you simplified $sqrt{z^2-1}$ as $z^2-1$ instead of $1-z^2$.
$endgroup$
– saulspatz
Dec 15 '18 at 15:31
$begingroup$
I agree up to the very last equal sign. How did you do the last integral? I'm guessing you simplified $sqrt{z^2-1}$ as $z^2-1$ instead of $1-z^2$.
$endgroup$
– saulspatz
Dec 15 '18 at 15:31
$begingroup$
the squrt of $(2z - 2)^2 $ is $ 2z-2 $ so doing the integral it is $ z^3/3 - 2z $
$endgroup$
– Mather
Dec 15 '18 at 15:33
$begingroup$
the squrt of $(2z - 2)^2 $ is $ 2z-2 $ so doing the integral it is $ z^3/3 - 2z $
$endgroup$
– Mather
Dec 15 '18 at 15:33
|
show 3 more comments
1 Answer
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$begingroup$
You are correct up to the last integral. Recall that $sqrt{z^2}=|z|,$ so $sqrt{(z^2-1)^2}=|z^2-1|$ When $-1le zle1,$ we have $|z^2-1|=1-z^2,$ so you've got the sign wrong.
$endgroup$
$begingroup$
oh i got it now thank you
$endgroup$
– Mather
Dec 15 '18 at 15:38
$begingroup$
It was my pleasure.
$endgroup$
– saulspatz
Dec 15 '18 at 15:40
add a comment |
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1 Answer
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$begingroup$
You are correct up to the last integral. Recall that $sqrt{z^2}=|z|,$ so $sqrt{(z^2-1)^2}=|z^2-1|$ When $-1le zle1,$ we have $|z^2-1|=1-z^2,$ so you've got the sign wrong.
$endgroup$
$begingroup$
oh i got it now thank you
$endgroup$
– Mather
Dec 15 '18 at 15:38
$begingroup$
It was my pleasure.
$endgroup$
– saulspatz
Dec 15 '18 at 15:40
add a comment |
$begingroup$
You are correct up to the last integral. Recall that $sqrt{z^2}=|z|,$ so $sqrt{(z^2-1)^2}=|z^2-1|$ When $-1le zle1,$ we have $|z^2-1|=1-z^2,$ so you've got the sign wrong.
$endgroup$
$begingroup$
oh i got it now thank you
$endgroup$
– Mather
Dec 15 '18 at 15:38
$begingroup$
It was my pleasure.
$endgroup$
– saulspatz
Dec 15 '18 at 15:40
add a comment |
$begingroup$
You are correct up to the last integral. Recall that $sqrt{z^2}=|z|,$ so $sqrt{(z^2-1)^2}=|z^2-1|$ When $-1le zle1,$ we have $|z^2-1|=1-z^2,$ so you've got the sign wrong.
$endgroup$
You are correct up to the last integral. Recall that $sqrt{z^2}=|z|,$ so $sqrt{(z^2-1)^2}=|z^2-1|$ When $-1le zle1,$ we have $|z^2-1|=1-z^2,$ so you've got the sign wrong.
answered Dec 15 '18 at 15:37
saulspatzsaulspatz
15.1k31330
15.1k31330
$begingroup$
oh i got it now thank you
$endgroup$
– Mather
Dec 15 '18 at 15:38
$begingroup$
It was my pleasure.
$endgroup$
– saulspatz
Dec 15 '18 at 15:40
add a comment |
$begingroup$
oh i got it now thank you
$endgroup$
– Mather
Dec 15 '18 at 15:38
$begingroup$
It was my pleasure.
$endgroup$
– saulspatz
Dec 15 '18 at 15:40
$begingroup$
oh i got it now thank you
$endgroup$
– Mather
Dec 15 '18 at 15:38
$begingroup$
oh i got it now thank you
$endgroup$
– Mather
Dec 15 '18 at 15:38
$begingroup$
It was my pleasure.
$endgroup$
– saulspatz
Dec 15 '18 at 15:40
$begingroup$
It was my pleasure.
$endgroup$
– saulspatz
Dec 15 '18 at 15:40
add a comment |
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$begingroup$
correct edited *
$endgroup$
– Mather
Dec 15 '18 at 15:12
$begingroup$
The integral looks right to me, and you certainly shouldn't get a negative answer. Please post your calculations, so we can pinpoint the error.
$endgroup$
– saulspatz
Dec 15 '18 at 15:15
$begingroup$
i have posted extended calculation
$endgroup$
– Mather
Dec 15 '18 at 15:28
$begingroup$
I agree up to the very last equal sign. How did you do the last integral? I'm guessing you simplified $sqrt{z^2-1}$ as $z^2-1$ instead of $1-z^2$.
$endgroup$
– saulspatz
Dec 15 '18 at 15:31
$begingroup$
the squrt of $(2z - 2)^2 $ is $ 2z-2 $ so doing the integral it is $ z^3/3 - 2z $
$endgroup$
– Mather
Dec 15 '18 at 15:33