Chapter 8: Applications of Triple Integration
Section 8.1: Volume
Example 8.1.5
Use an iterated triple integral to obtain the volume of the region R, the wedge the planes z=y and z=0 cut from the cylinder x2+y2=4.
Solution
Mathematical Solution
Figure 8.1.5(a) shows the wedge whose volume is obtained by iterating a triple integral in cylindrical coordinates in the order dz dr dθ.
∫0π∫02∫0r sinθr dz dr dθ = 163
(The integration in the z-direction is from z=0 to z=y=r sinθ.)
Figure 8.1.5(a) Wedge
Maple Solution - Interactive
Table 8.1.5(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≻Cylindrical
Evaluate ∭RΨr,θ,z dv and Graph R
Volume Element dv
r dz dr dθ
r dz dθ dr
r dr dθ dz
r dr dz dθ
r dθ dr dz
r dθ dz dr
, where Ψ=
F=
G=
b=
f=
g=
a=
Table 8.1.5(a) Task template integrating in cylindrical coordinates
Since the iteration order can be taken as dz dr dθ, the task template in Table 8.1.5(a), using the MultiInt command from the Student MultivariateCalculus package, applies.
Tools≻Tasks≻Browse: Calculus - Multivariate≻Integration≻Multiple Integration≻Cylindrical
Iterated Triple Integral in Cylindrical Coordinates
Integrand:
1
Region: z1r,θ≤z≤z2r,θ,r1θ≤r≤r2θ,a≤θ≤b
z1r,θ
0
z2r,θ
r sinθ
r⁢sin⁡θ
r1θ
r2θ
2
a
b
π
π
Inert Integral: dz dr dθ
(Note automatic insertion of Jacobian.)
StudentMultivariateCalculusMultiInt,z=..,r=..,θ=..,coordinates=cylindricalr,θ,z,output=integral
∫0π∫02∫0r⁢sin⁡θrⅆzⅆrⅆθ
Value:
StudentMultivariateCalculusMultiInt,z=..,r=..,θ=..,coordinates=cylindricalr,θ,z
163
Stepwise Evaluation:
StudentMultivariateCalculusMultiInt,z=..,r=..,θ=..,coordinates=cylindricalr,θ,z,output=steps
∫0π∫02∫0r⁢sin⁡θrⅆzⅆrⅆθ=∫0π∫02r⁢zz=0..r⁢sin⁡θ|r⁢zz=0..r⁢sin⁡θⅆrⅆθ=∫0π∫02r2⁢sin⁡θⅆrⅆθ=∫0πr3⁢sin⁡θ3r=0..2|r3⁢sin⁡θ3r=0..2ⅆθ=∫0π8⁢sin⁡θ3ⅆθ=−8⁢cos⁡θ3θ=0..π|−8⁢cos⁡θ3θ=0..π
Table 8.1.5(b) Task template implementing the MultiInt command iterating in the order dz dr dθ
Table 8.1.5(c) provides a solution from first principles.
Calculus Palette: Iterated triple-integral template
Context Panel: Evaluate and Display Inline
∫0π∫02∫0r sinθr ⅆz ⅆr ⅆθ = 163
Table 8.1.5(c) Integration via first principles
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∫0π∫02∫0r⁢sin⁡θrⅆzⅆrⅆθ=163
Maple Solution - Coded
Table 8.1.5(d) obtains a solution via the MultiInt command in the Student MultivariateCalculus package. See Table 8.1.5(b) for an implementation of the integration via a task template.
Install the Student MultivariateCalculus package.
withStudent:-MultivariateCalculus:
MultiInt1,z=0..r sinθ,r=0..2,θ=0.. π,coordinates=cylindricalr,θ,z,output=integral
MultiInt1,z=0..r sinθ,r=0..2,θ=0..π,coordinates=cylindricalr,θ,z = 163
Table 8.1.5(d) MultiInt command iterating in cylindrical coordinates in the order dz dr dθ
Table 8.1.5(e) implements the iterated integration via the top-level Int and int commands.
Intr,z=0..r sinθ,r=0..2,θ=0.. π=intr,z=0..r sinθ,r=0..2,θ=0.. π
∫0π∫02∫0r⁢sin⁡θrⅆzⅆrⅆθ=163
Table 8.1.5(e) Top-level Int and int commands
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