Find the volume of the solid formed by rotating about the $x$-axis
$begingroup$
Find the volume of the solid formed by rotating the region enclosed by the curves $y=(e^ x) + 2$, $y=0$ , $x=0$, and $x=0.7$ about the $x$-axis
I set up the equations as follows using the washer method. I'm not sure if I'm setting it up right or using the correct method.
$$int_0^{0.7} pi (e^x+2)^2dx$$
calculus volume
$endgroup$
add a comment |
$begingroup$
Find the volume of the solid formed by rotating the region enclosed by the curves $y=(e^ x) + 2$, $y=0$ , $x=0$, and $x=0.7$ about the $x$-axis
I set up the equations as follows using the washer method. I'm not sure if I'm setting it up right or using the correct method.
$$int_0^{0.7} pi (e^x+2)^2dx$$
calculus volume
$endgroup$
1
$begingroup$
The setup is correct. To finish, expand $(e^x+2)^2$ and integrate.
$endgroup$
– André Nicolas
Feb 3 '14 at 19:37
1
$begingroup$
Note you can pull the $pi$ out of the integral.
$endgroup$
– AlexR
Feb 3 '14 at 19:37
add a comment |
$begingroup$
Find the volume of the solid formed by rotating the region enclosed by the curves $y=(e^ x) + 2$, $y=0$ , $x=0$, and $x=0.7$ about the $x$-axis
I set up the equations as follows using the washer method. I'm not sure if I'm setting it up right or using the correct method.
$$int_0^{0.7} pi (e^x+2)^2dx$$
calculus volume
$endgroup$
Find the volume of the solid formed by rotating the region enclosed by the curves $y=(e^ x) + 2$, $y=0$ , $x=0$, and $x=0.7$ about the $x$-axis
I set up the equations as follows using the washer method. I'm not sure if I'm setting it up right or using the correct method.
$$int_0^{0.7} pi (e^x+2)^2dx$$
calculus volume
calculus volume
edited Feb 3 '14 at 19:37
AlexR
22.8k12349
22.8k12349
asked Feb 3 '14 at 19:35
jannyjanny
951412
951412
1
$begingroup$
The setup is correct. To finish, expand $(e^x+2)^2$ and integrate.
$endgroup$
– André Nicolas
Feb 3 '14 at 19:37
1
$begingroup$
Note you can pull the $pi$ out of the integral.
$endgroup$
– AlexR
Feb 3 '14 at 19:37
add a comment |
1
$begingroup$
The setup is correct. To finish, expand $(e^x+2)^2$ and integrate.
$endgroup$
– André Nicolas
Feb 3 '14 at 19:37
1
$begingroup$
Note you can pull the $pi$ out of the integral.
$endgroup$
– AlexR
Feb 3 '14 at 19:37
1
1
$begingroup$
The setup is correct. To finish, expand $(e^x+2)^2$ and integrate.
$endgroup$
– André Nicolas
Feb 3 '14 at 19:37
$begingroup$
The setup is correct. To finish, expand $(e^x+2)^2$ and integrate.
$endgroup$
– André Nicolas
Feb 3 '14 at 19:37
1
1
$begingroup$
Note you can pull the $pi$ out of the integral.
$endgroup$
– AlexR
Feb 3 '14 at 19:37
$begingroup$
Note you can pull the $pi$ out of the integral.
$endgroup$
– AlexR
Feb 3 '14 at 19:37
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
Your equation is correct.
$$begin{align*}
A & = pi int_0^{0.7} (e^x + 2)^2 dx = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4cdot0.7 right)\
& = pi left( frac12 int_0^{1.4} e^x dx + int_0^{0.7} e^x dx + 2.8right)\
& = pi left( frac12 e^{1.4} + e^{0.7} + 2.8 right) \
& approx 21.4927ldots
end{align*}$$
$endgroup$
$begingroup$
Not sure your answer is correct. Note $e^0ne0$.
$endgroup$
– John Molokach
Jan 9 '16 at 14:59
$begingroup$
@JohnMolokach $e^0 = 1$ by definition...
$endgroup$
– AlexR
Jan 9 '16 at 15:00
$begingroup$
Sorry, edited...
$endgroup$
– John Molokach
Jan 9 '16 at 15:01
$begingroup$
It might be me, but are you sure you can make the simplification of taking $e^{2x}$ out to the range over which you're integrating? As if you leave it in and integrate, it integrates to $e^2x^2$ so you wouldn't simply be evaluating $e^x$ between $0$ and $1.4$. I'm not entirely sure that gives the same answer.
$endgroup$
– user334732
May 17 '18 at 10:46
$begingroup$
@RobertFrost That‘s a substitution, yielding the factor of $1/2$
$endgroup$
– AlexR
May 17 '18 at 11:18
|
show 2 more comments
$begingroup$
Your setting up was all correct. However you can conveniently integrate with symbols and get on with integration to go to numerical work in the last stages of calculation by plugging in constants. Also bring out constants to LHS at the earliest, else that keeps dragging on till the end.
$$begin{align*}
A/pi & = int_0^{a} (e^x + c)^2 dx = int_0^{a} e^{2x} dx + 2c int_0^{a} e^x dx + c^2 a\
& = frac12 ( e^{2a}-1) + 2c(e^{a}-1) dx + ac^2.\
end{align*}$$
$endgroup$
add a comment |
$begingroup$
As this just got bumped from the homepage and @AlexR' answer is not correct, here the correct answer
begin{align*}
A & = pi int_0^{0.7} (e^x + 2)^2 dx = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4int_0^{0.7}dxright)\
& = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4cdot0.7 right)\
& = pi left( frac12 int_0^{1.4} e^x dx + 4int_0^{0.7} e^x dx + 2.8right)qquad qquad(u=2x,du=2dx)\
& = pi left( frac12 left(e^{1.4}-e^0right) + 4left(e^{0.7}-e^0right) + 2.8 right) \
& approx 26.3347ldots
end{align*}
$endgroup$
add a comment |
Your Answer
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3 Answers
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3 Answers
3
active
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votes
$begingroup$
Your equation is correct.
$$begin{align*}
A & = pi int_0^{0.7} (e^x + 2)^2 dx = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4cdot0.7 right)\
& = pi left( frac12 int_0^{1.4} e^x dx + int_0^{0.7} e^x dx + 2.8right)\
& = pi left( frac12 e^{1.4} + e^{0.7} + 2.8 right) \
& approx 21.4927ldots
end{align*}$$
$endgroup$
$begingroup$
Not sure your answer is correct. Note $e^0ne0$.
$endgroup$
– John Molokach
Jan 9 '16 at 14:59
$begingroup$
@JohnMolokach $e^0 = 1$ by definition...
$endgroup$
– AlexR
Jan 9 '16 at 15:00
$begingroup$
Sorry, edited...
$endgroup$
– John Molokach
Jan 9 '16 at 15:01
$begingroup$
It might be me, but are you sure you can make the simplification of taking $e^{2x}$ out to the range over which you're integrating? As if you leave it in and integrate, it integrates to $e^2x^2$ so you wouldn't simply be evaluating $e^x$ between $0$ and $1.4$. I'm not entirely sure that gives the same answer.
$endgroup$
– user334732
May 17 '18 at 10:46
$begingroup$
@RobertFrost That‘s a substitution, yielding the factor of $1/2$
$endgroup$
– AlexR
May 17 '18 at 11:18
|
show 2 more comments
$begingroup$
Your equation is correct.
$$begin{align*}
A & = pi int_0^{0.7} (e^x + 2)^2 dx = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4cdot0.7 right)\
& = pi left( frac12 int_0^{1.4} e^x dx + int_0^{0.7} e^x dx + 2.8right)\
& = pi left( frac12 e^{1.4} + e^{0.7} + 2.8 right) \
& approx 21.4927ldots
end{align*}$$
$endgroup$
$begingroup$
Not sure your answer is correct. Note $e^0ne0$.
$endgroup$
– John Molokach
Jan 9 '16 at 14:59
$begingroup$
@JohnMolokach $e^0 = 1$ by definition...
$endgroup$
– AlexR
Jan 9 '16 at 15:00
$begingroup$
Sorry, edited...
$endgroup$
– John Molokach
Jan 9 '16 at 15:01
$begingroup$
It might be me, but are you sure you can make the simplification of taking $e^{2x}$ out to the range over which you're integrating? As if you leave it in and integrate, it integrates to $e^2x^2$ so you wouldn't simply be evaluating $e^x$ between $0$ and $1.4$. I'm not entirely sure that gives the same answer.
$endgroup$
– user334732
May 17 '18 at 10:46
$begingroup$
@RobertFrost That‘s a substitution, yielding the factor of $1/2$
$endgroup$
– AlexR
May 17 '18 at 11:18
|
show 2 more comments
$begingroup$
Your equation is correct.
$$begin{align*}
A & = pi int_0^{0.7} (e^x + 2)^2 dx = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4cdot0.7 right)\
& = pi left( frac12 int_0^{1.4} e^x dx + int_0^{0.7} e^x dx + 2.8right)\
& = pi left( frac12 e^{1.4} + e^{0.7} + 2.8 right) \
& approx 21.4927ldots
end{align*}$$
$endgroup$
Your equation is correct.
$$begin{align*}
A & = pi int_0^{0.7} (e^x + 2)^2 dx = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4cdot0.7 right)\
& = pi left( frac12 int_0^{1.4} e^x dx + int_0^{0.7} e^x dx + 2.8right)\
& = pi left( frac12 e^{1.4} + e^{0.7} + 2.8 right) \
& approx 21.4927ldots
end{align*}$$
answered Feb 3 '14 at 19:41
AlexRAlexR
22.8k12349
22.8k12349
$begingroup$
Not sure your answer is correct. Note $e^0ne0$.
$endgroup$
– John Molokach
Jan 9 '16 at 14:59
$begingroup$
@JohnMolokach $e^0 = 1$ by definition...
$endgroup$
– AlexR
Jan 9 '16 at 15:00
$begingroup$
Sorry, edited...
$endgroup$
– John Molokach
Jan 9 '16 at 15:01
$begingroup$
It might be me, but are you sure you can make the simplification of taking $e^{2x}$ out to the range over which you're integrating? As if you leave it in and integrate, it integrates to $e^2x^2$ so you wouldn't simply be evaluating $e^x$ between $0$ and $1.4$. I'm not entirely sure that gives the same answer.
$endgroup$
– user334732
May 17 '18 at 10:46
$begingroup$
@RobertFrost That‘s a substitution, yielding the factor of $1/2$
$endgroup$
– AlexR
May 17 '18 at 11:18
|
show 2 more comments
$begingroup$
Not sure your answer is correct. Note $e^0ne0$.
$endgroup$
– John Molokach
Jan 9 '16 at 14:59
$begingroup$
@JohnMolokach $e^0 = 1$ by definition...
$endgroup$
– AlexR
Jan 9 '16 at 15:00
$begingroup$
Sorry, edited...
$endgroup$
– John Molokach
Jan 9 '16 at 15:01
$begingroup$
It might be me, but are you sure you can make the simplification of taking $e^{2x}$ out to the range over which you're integrating? As if you leave it in and integrate, it integrates to $e^2x^2$ so you wouldn't simply be evaluating $e^x$ between $0$ and $1.4$. I'm not entirely sure that gives the same answer.
$endgroup$
– user334732
May 17 '18 at 10:46
$begingroup$
@RobertFrost That‘s a substitution, yielding the factor of $1/2$
$endgroup$
– AlexR
May 17 '18 at 11:18
$begingroup$
Not sure your answer is correct. Note $e^0ne0$.
$endgroup$
– John Molokach
Jan 9 '16 at 14:59
$begingroup$
Not sure your answer is correct. Note $e^0ne0$.
$endgroup$
– John Molokach
Jan 9 '16 at 14:59
$begingroup$
@JohnMolokach $e^0 = 1$ by definition...
$endgroup$
– AlexR
Jan 9 '16 at 15:00
$begingroup$
@JohnMolokach $e^0 = 1$ by definition...
$endgroup$
– AlexR
Jan 9 '16 at 15:00
$begingroup$
Sorry, edited...
$endgroup$
– John Molokach
Jan 9 '16 at 15:01
$begingroup$
Sorry, edited...
$endgroup$
– John Molokach
Jan 9 '16 at 15:01
$begingroup$
It might be me, but are you sure you can make the simplification of taking $e^{2x}$ out to the range over which you're integrating? As if you leave it in and integrate, it integrates to $e^2x^2$ so you wouldn't simply be evaluating $e^x$ between $0$ and $1.4$. I'm not entirely sure that gives the same answer.
$endgroup$
– user334732
May 17 '18 at 10:46
$begingroup$
It might be me, but are you sure you can make the simplification of taking $e^{2x}$ out to the range over which you're integrating? As if you leave it in and integrate, it integrates to $e^2x^2$ so you wouldn't simply be evaluating $e^x$ between $0$ and $1.4$. I'm not entirely sure that gives the same answer.
$endgroup$
– user334732
May 17 '18 at 10:46
$begingroup$
@RobertFrost That‘s a substitution, yielding the factor of $1/2$
$endgroup$
– AlexR
May 17 '18 at 11:18
$begingroup$
@RobertFrost That‘s a substitution, yielding the factor of $1/2$
$endgroup$
– AlexR
May 17 '18 at 11:18
|
show 2 more comments
$begingroup$
Your setting up was all correct. However you can conveniently integrate with symbols and get on with integration to go to numerical work in the last stages of calculation by plugging in constants. Also bring out constants to LHS at the earliest, else that keeps dragging on till the end.
$$begin{align*}
A/pi & = int_0^{a} (e^x + c)^2 dx = int_0^{a} e^{2x} dx + 2c int_0^{a} e^x dx + c^2 a\
& = frac12 ( e^{2a}-1) + 2c(e^{a}-1) dx + ac^2.\
end{align*}$$
$endgroup$
add a comment |
$begingroup$
Your setting up was all correct. However you can conveniently integrate with symbols and get on with integration to go to numerical work in the last stages of calculation by plugging in constants. Also bring out constants to LHS at the earliest, else that keeps dragging on till the end.
$$begin{align*}
A/pi & = int_0^{a} (e^x + c)^2 dx = int_0^{a} e^{2x} dx + 2c int_0^{a} e^x dx + c^2 a\
& = frac12 ( e^{2a}-1) + 2c(e^{a}-1) dx + ac^2.\
end{align*}$$
$endgroup$
add a comment |
$begingroup$
Your setting up was all correct. However you can conveniently integrate with symbols and get on with integration to go to numerical work in the last stages of calculation by plugging in constants. Also bring out constants to LHS at the earliest, else that keeps dragging on till the end.
$$begin{align*}
A/pi & = int_0^{a} (e^x + c)^2 dx = int_0^{a} e^{2x} dx + 2c int_0^{a} e^x dx + c^2 a\
& = frac12 ( e^{2a}-1) + 2c(e^{a}-1) dx + ac^2.\
end{align*}$$
$endgroup$
Your setting up was all correct. However you can conveniently integrate with symbols and get on with integration to go to numerical work in the last stages of calculation by plugging in constants. Also bring out constants to LHS at the earliest, else that keeps dragging on till the end.
$$begin{align*}
A/pi & = int_0^{a} (e^x + c)^2 dx = int_0^{a} e^{2x} dx + 2c int_0^{a} e^x dx + c^2 a\
& = frac12 ( e^{2a}-1) + 2c(e^{a}-1) dx + ac^2.\
end{align*}$$
edited Apr 25 '17 at 11:23
answered Apr 25 '17 at 9:39
NarasimhamNarasimham
21.2k62258
21.2k62258
add a comment |
add a comment |
$begingroup$
As this just got bumped from the homepage and @AlexR' answer is not correct, here the correct answer
begin{align*}
A & = pi int_0^{0.7} (e^x + 2)^2 dx = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4int_0^{0.7}dxright)\
& = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4cdot0.7 right)\
& = pi left( frac12 int_0^{1.4} e^x dx + 4int_0^{0.7} e^x dx + 2.8right)qquad qquad(u=2x,du=2dx)\
& = pi left( frac12 left(e^{1.4}-e^0right) + 4left(e^{0.7}-e^0right) + 2.8 right) \
& approx 26.3347ldots
end{align*}
$endgroup$
add a comment |
$begingroup$
As this just got bumped from the homepage and @AlexR' answer is not correct, here the correct answer
begin{align*}
A & = pi int_0^{0.7} (e^x + 2)^2 dx = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4int_0^{0.7}dxright)\
& = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4cdot0.7 right)\
& = pi left( frac12 int_0^{1.4} e^x dx + 4int_0^{0.7} e^x dx + 2.8right)qquad qquad(u=2x,du=2dx)\
& = pi left( frac12 left(e^{1.4}-e^0right) + 4left(e^{0.7}-e^0right) + 2.8 right) \
& approx 26.3347ldots
end{align*}
$endgroup$
add a comment |
$begingroup$
As this just got bumped from the homepage and @AlexR' answer is not correct, here the correct answer
begin{align*}
A & = pi int_0^{0.7} (e^x + 2)^2 dx = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4int_0^{0.7}dxright)\
& = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4cdot0.7 right)\
& = pi left( frac12 int_0^{1.4} e^x dx + 4int_0^{0.7} e^x dx + 2.8right)qquad qquad(u=2x,du=2dx)\
& = pi left( frac12 left(e^{1.4}-e^0right) + 4left(e^{0.7}-e^0right) + 2.8 right) \
& approx 26.3347ldots
end{align*}
$endgroup$
As this just got bumped from the homepage and @AlexR' answer is not correct, here the correct answer
begin{align*}
A & = pi int_0^{0.7} (e^x + 2)^2 dx = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4int_0^{0.7}dxright)\
& = pi left( int_0^{0.7} e^{2x} dx + 4 int_0^{0.7} e^x dx + 4cdot0.7 right)\
& = pi left( frac12 int_0^{1.4} e^x dx + 4int_0^{0.7} e^x dx + 2.8right)qquad qquad(u=2x,du=2dx)\
& = pi left( frac12 left(e^{1.4}-e^0right) + 4left(e^{0.7}-e^0right) + 2.8 right) \
& approx 26.3347ldots
end{align*}
answered Nov 28 '18 at 10:53
Bo5manBo5man
518
518
add a comment |
add a comment |
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1
$begingroup$
The setup is correct. To finish, expand $(e^x+2)^2$ and integrate.
$endgroup$
– André Nicolas
Feb 3 '14 at 19:37
1
$begingroup$
Note you can pull the $pi$ out of the integral.
$endgroup$
– AlexR
Feb 3 '14 at 19:37