Chapter 8: Applications of Triple Integration
Section 8.1: Volume
Example 8.1.24
Use an iterated triple integral to obtain the volume of R, the region bounded above by the surface z=10 y, and below by the surface z=2 x2+3 y2.
Solution
Mathematical Solution
Figure 8.1.24(a) shows the solid whose volume is obtained by iterating a triple integral in Cartesian coordinates in the order dy dz dx.
∫0103∫−5 y−3 y2/25 y−3 y2/2∫2 x2+3 y210 y1 dz dx dy = 625108⁢6⁢π
The ellipse in Figure 8.1.24(b) is the projection of R onto the xy-plane. It is the graph of 2 x2+3 y2=10 y. This equation, and its graph, determined the order of iteration: the equation is easier to solve for x than for y. Hence, the integration in x is done before that in y.
Figure 8.1.24(a) Paraboloid and plane
Figure 8.1.24(b) Elliptic projection onto z=0
Maple Solution - Interactive
Initialize
Tools≻Load Package: Student Multivariate Calculus
Loading Student:-MultivariateCalculus
Access the MultiInt command via the Context Panel
a=5 y−3 y2/2→assign
b=2 x2+3 y2→assign
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∫0103∫−−6⁢y2+20⁢y2−6⁢y2+20⁢y2∫2⁢x2+3⁢y210⁢y1ⅆzⅆxⅆy=625⁢6⁢π108
Table 8.1.24(a) provides a solution by a task template that integrates in Cartesian coordinates and draws the region of integration.
Tools≻Tasks≻Browse: 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 8.1.24(a) Task template integrating in Cartesian coordinates
Table 8.1.24(b) provides a solution from first principles.
Calculus Palette: Iterated triple-integral template
Context Panel: Evaluate and Display Inline
∫0103∫−5 y−2 y25 y−32 y2∫2 x2+3 y210 y1 ⅆz ⅆx ⅆy = 8125⁢2⁢π2048+625⁢2⁢3⁢π216+1076875⁢I⁢2124416−8125⁢2⁢arccos⁡532048
Table 8.1.24(b) Integration via first principles
Maple Solution - Coded
Table 8.1.24(c) obtains a solution via the MultiInt command in the Student MultivariateCalculus package.
Install the Student MultivariateCalculus package.
withStudent:-MultivariateCalculus:
MultiInt1,z=2 x2+3 y2..10 y,x=−5 y−3 y2/2..5 y−3 y2/2,y=0..10/3,output=integral
∫0103∫−−6⁢y2+20⁢y2−6⁢y2+20⁢y2∫2⁢x2+3⁢y210⁢y1ⅆzⅆxⅆy
MultiInt1,z=2 x2+3 y2..10 y,x=−5 y−3 y2/2..5 y−3 y2/2,y=0..10/3 = 625⁢6⁢π108
Table 8.1.4(c) MultiInt command iterating in Cartesian coordinates in the order dz dx dy
Table 8.1.24(d) implements the iterated integration via the top-level Int and int commands.
Int1,z=2 x2+3 y2..10 y,x=−5 y−3 y2/2..5 y−3 y2/2,y=0..10/3=int1,z=2 x2+3 y2..10 y,x=−5 y−3 y2/2..5 y−3 y2/2,y=0..10/3
∫0103∫−−6⁢y2+20⁢y2−6⁢y2+20⁢y2∫2⁢x2+3⁢y210⁢y1ⅆzⅆxⅆy=625⁢6⁢π108
Table 8.1.24(d) Top-level Int and int commands
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