Chapter 8: Applications of Triple Integration
Section 8.1: Volume
Example 8.1.21
Use an iterated triple integral to obtain the volume of R, the region enclosed by the surface ρ=1−cosφ, where ρ,φ,θ are the variables in spherical coordinates.
Solution
Mathematical Solution
Figure 8.1.21(a) shows the solid whose volume is obtained by iterating a triple integral in spherical coordinates in the order dρ dφ dθ.
∫02 π∫0π∫01−cosφρ2sinφ dρ dφ dθ = 83 π
Figure 8.1.21(a) Region R
Maple Solution - Interactive
Table 8.1.21(a) provides a solution by a task template that integrates in cylindrical coordinates and draws the region of integration.
Tools≻Tasks≻Browse: Calculus - Multivariate≻Integration≻Visualizing Regions of Integration≻Spherical
Evaluate ∭RΨρ,φ,θ dv and Graph R
Volume Element dv=ρ2sinφ×
dρ dφ dθ
dρ dθ dφ
dφ dρ dθ
dφ dθ dρ
dθ dφ dρ
dθ dρ dφ
, where Ψ=
F=
G=
b=
f=
g=
a=
Table 8.1.21(a) Task template integrating in spherical coordinates
Since the iteration order can be taken as dρ dφ dθ, the task template in Table 8.1.21(a), using the MultiInt command from the Student MultivariateCalculus package, applies.
Tools≻Tasks≻Browse: Calculus - Multivariate≻Integration≻Multiple Integration≻Spherical
Iterated Triple Integral in Spherical Coordinates
(φ = colatitude, measured down from z-axis)
Integrand:
1
Region: ρ1φ,θ≤ρ≤ρ2φ,θ,φ1θ≤φ≤φ2θ,a≤θ≤b
ρ1φ,θ
0
ρ2φ,θ
1−cosφ
1−cos⁡φ
φ1θ
φ2θ
π
π
a
b
2 π
2⁢π
Inert Integral: dρ dφ dθ
StudentMultivariateCalculusMultiInt,ρ=..,φ=..,θ=..,coordinates=sphericalρ,φ,θ,output=integral
∫02⁢π∫0π∫01−cos⁡φρ2⁢sin⁡φⅆρⅆφⅆθ
Value:
StudentMultivariateCalculusMultiInt,ρ=..,φ=..,θ=.., coordinates=sphericalρ,φ,θ
8⁢π3
Stepwise Evaluation:
StudentMultivariateCalculusMultiInt,ρ=.., φ=..,θ=..,coordinates=sphericalρ,φ,θ,output=steps
∫02⁢π∫0π∫01−cos⁡φρ2⁢sin⁡φⅆρⅆφⅆθ=∫02⁢π∫0πρ3⁢sin⁡φ3ρ=0..1−cos⁡φ|ρ3⁢sin⁡φ3ρ=0..1−cos⁡φⅆφⅆθ=∫02⁢π∫0πsin⁡φ⁢1−cos⁡φ33ⅆφⅆθ=∫02⁢π1−cos⁡φ412φ=0..π|1−cos⁡φ412φ=0..πⅆθ=∫02⁢π43ⅆθ=4⁢θ3θ=0..2⁢π|4⁢θ3θ=0..2⁢π
Table 8.1.21(b) Task template implementing the MultiInt command iterating in the order dρ dφ dθ
Initialize
Tools≻Load Package: Student Multivariate Calculus
Loading Student:-MultivariateCalculus
Access the MultiInt command via the Context Panel
Type the integrand, 1.
Context Panel: Student Multivariate Calculus≻Integrate≻Iterated Fill in the fields of the two dialogs shown below.
Context Panel: Evaluate Integral
1→MultiInt∫02⁢π∫0π∫01−cos⁡φρ2⁢sin⁡φⅆρⅆφⅆθ=8⁢π3
Table 8.1.21(c) provides a solution from first principles.
Calculus Palette: Iterated triple-integral template
Context Panel: Evaluate and Display Inline
∫02 π∫0π∫01−cosφρ2sinφ ⅆρ ⅆφ ⅆθ = 8⁢π3
Table 8.1.21(c) Integration via first principles
Maple Solution - Coded
Table 8.1.21(d) obtains a solution via the MultiInt command in the Student MultivariateCalculus package. See Table 8.1.21(b) for an implementation of this integration via a task template.
Install the Student MultivariateCalculus package.
withStudent:-MultivariateCalculus:
MultiInt1,ρ=0..1−cosφ,φ=0..π,θ=0..2 π,coordinates=sphericalρ,φ,θ,output=integral
MultiInt1,ρ=0..1−cosφ,φ=0..π,θ=0..2 π,coordinates=sphericalρ,φ,θ = 8⁢π3
Table 8.1.21(d) MultiInt command iterating in spherical coordinates in the order dρ dφ dθ
Table 8.1.21(e) implements the iterated integration via the top-level Int and int commands.
Intρ2sinφ,ρ=0..1−cosφ,φ=0..π,θ=0..2 π=intρ2sinφ,ρ=0..1−cosφ,φ=0..π,θ=0..2 π
∫02⁢π∫0π∫01−cos⁡φρ2⁢sin⁡φⅆρⅆφⅆθ=8⁢π3
Table 8.1.21(e) Top-level Int and int commands
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