Chapter 7: Triple Integration
Section 7.2: Iterated Triple Integrals
Example 7.2.3
fx,y,z=1+2 x2+3 y2+4 z2; R={x,y,z| x∈1,2,y∈−1,3,z∈2,4}.
See Example 7.1.3.
Solution
Mathematical Solution
For the given triple integral, Table 7.2.3 lists its six iterations in Cartesian coordinates.
∫x=1x=2∫y=−1y=3∫z=2z=4fx,y,z dz dy dx=400
∫y=−1y=3∫x=1x=2∫z=2z=4fx,y,z dz dx dy=400
∫z=2z=4∫x=1x=2∫y=−1y=3fx,y,z dy dx dz=400
∫x=1x=2∫z=2z=4∫y=−1y=3fx,y,z dy dz dx=400
∫z=2z=4∫y=−1y=3∫x=1x=2fx,y,z dx dy dz=400
∫y=−1y=3∫z=2z=4∫x=1x=2fx,y,z dx dz dy=400
Table 7.2.3(a) In Cartesian coordinates, the six iterations of a given triple integral
One possible iteration of the triple integral, evaluated stepwise, is given in Table 7.2.2(b).
∫12∫−13∫241+2 x2+3 y2+4 z2 dz dy dx
=∫12∫−132 x2+3 y2z+4 z33+zz=2z=4 dy dx
=∫12∫−132 x2+3 y24−2+4343−23+4−2 dy dx
=∫12∫−132303+4 x2+6 y2 dy dx
=∫124 x2y+6 y33+2303yy=−1y=3 dx
=∫124 x23−−1+233−−13+23033−−1 dx
=∫1210883+16 x2 dx
=10883x+16x33x=1x=2
=108832−1+16323−13
=12003=400
Table 7.2.3(b) Stepwise evaluation of the dz dy dx iteration
Maple Solution - Interactive
Define the integrand f
Context Panel: Assign Name
f=1+2 x2+3 y2+4 z2→assign
Write and evaluate all six iterations of the triple integral
Calculus palette: Iterated triple-integral palette
Context Panel: Evaluate and Display Inline
∫12∫−13∫24f ⅆz ⅆy ⅆx = 400
∫−13∫12∫24f ⅆz ⅆx ⅆy = 400
∫24∫12∫−13f ⅆy ⅆx ⅆz = 400
∫12∫24∫−13f ⅆy ⅆz ⅆx = 400
∫24∫−13∫12f ⅆx ⅆy ⅆz = 400
∫−13∫24∫12f ⅆx ⅆz ⅆy = 400
Table 7.2.3(c) provides a solution via a task template that integrates in the order dx dy dz. This template implements the modified int command from the Student VectorCalculus package in which a parallelepiped is recognized as a predefined region.
Tools≻Tasks≻Browse:
Calculus - Vector≻Integration≻Multiple Integration≻3-D≻Over a Cube
Integrate fx,y,z over a Cube
fx,y,z=
∫z1z2∫y1y2∫x1x2f ⅆx ⅆy ⅆz
x2=
y2=
z2=
x1=
y1=
z1=
dx dy dz
Table 7.2.3(c) Solution by task template
Table 7.2.3(d) provides a solution via a task template designed to evaluate an iterated triple-integral, and to visualize the spatial region over which the integration takes place. It is based on the MultiInt command in the Student MultivariateCalculus package, but the graphics are coded from first principles.
The iteration order chosen for the table is dz dy dx, but the task template admits all six possible iterations.
Calculus - Multivariate≻Integration≻Visualizing Regions of Integration≻Cartesian 3-D
Evaluate ∭RΨx,y,z dv and Graph R
Volume Element dv
Select dvdz dy dxdz dx dydx dy dzdx dz dydy dx dzdy dz dx
, where Ψ=
F=
G=
b=
f=
g=
a=
Table 7.2.3(d) Task template for visualizing regions of integration
Maple Solution - Coded
Initialize
Define the integrand f.
f≔1+2 x2+3 y2+4 z2:
Use the Int command to display the unevaluated integral, and the int command to obtain its value.
Intf,z=2..4,y=−1..3,x=1..2=intf,z=2..4,y=−1..3,x=1..2
∫12∫−13∫242⁢x2+3⁢y2+4⁢z2+1ⅆzⅆyⅆx=400
Intf,z=2..4,x=1..2,y=−1..3=intf,z=2..4,x=1..2,y=−1..3
∫−13∫12∫242⁢x2+3⁢y2+4⁢z2+1ⅆzⅆxⅆy=400
Intf,y=−1..3,x=1..2,z=2..4=intf,y=−1..3,x=1..2,z=2..4
∫24∫12∫−132⁢x2+3⁢y2+4⁢z2+1ⅆyⅆxⅆz=400
Intf,y=−1..3,z=2..4,x=1..2=intf,y=−1..3,z=2..4,x=1..2
∫12∫24∫−132⁢x2+3⁢y2+4⁢z2+1ⅆyⅆzⅆx=400
Intf,x=1..2,y=−1..3,z=2..4=intf,x=1..2,y=−1..3,z=2..4
∫24∫−13∫122⁢x2+3⁢y2+4⁢z2+1ⅆxⅆyⅆz=400
Intf,x=1..2,z=2..4,y=−1..3=intf,x=1..2,z=2..4,y=−1..3
∫−13∫24∫122⁢x2+3⁢y2+4⁢z2+1ⅆxⅆzⅆy=400
The option "output = steps" will cause the MultiInt command in the Student MultivariateCalculus package to return the steps in the evaluation of an iterated triple-integral. The case of iteration in the order dz dy dx is given in Table 7.2.3(e).
Student:-MultivariateCalculus:-MultiIntf,z=2..4,y=−1..3,x=1..2,output=steps
400
Table 7.2.3(e) Stepwise evaluation of an iterated triple-integral
Table 7.2.3(f) contains the implementation of the Parallelepiped option in the MultiInt command as modified in the Student MultivariateCalculus package. The order of the variables in the list to the left of "Parallelepiped" determines the order of iteration in the triple integral.
Install the Student MultivariateCalculus package.
withStudent:-MultivariateCalculus:
MultiIntf,x,y,z=Parallelepiped1..2,−1..3,2..4,output=integral
∫24∫−13∫122⁢x2+3⁢y2+4⁢z2+1ⅆxⅆyⅆz
MultiIntf,x,y,z=Parallelepiped1..2,−1..3,2..4 = 400
Table 7.2.3(f) The Parallelepiped option in the MultiInt command, Student MultivariateCalculus
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