Upper and lower bounds of a triple integral

Click For Summary
SUMMARY

The discussion focuses on determining the upper and lower bounds of a triple integral defined over a region T in the first octant, bounded by the surfaces y = √x and z = 1 - y. The integral is expressed as iterated integrals in three different orders: dy dx dz, dx dy dz, and dz dx dy. The correct bounds for these integrals were derived, with specific attention to the relationships between x, y, and z, leading to the final forms: ∫₀¹ ∫₀¹⁻ᶻ ∫₀^{y²} f(x,y,z) dx dy dz, ∫₀¹ ∫₀^{(1-z)²} ∫_{√x}¹ f(x,y,z) dy dx dz, and ∫₀¹ ∫₀^{y²} ∫₀^{1-y} f(x,y,z) dz dx dy.

PREREQUISITES
  • Understanding of triple integrals in multivariable calculus
  • Familiarity with the concept of bounded regions in R³
  • Knowledge of surface equations such as y = √x and z = 1 - y
  • Proficiency in MATLAB for visualizing mathematical functions
NEXT STEPS
  • Study the properties of triple integrals in multivariable calculus
  • Learn how to visualize 3D surfaces and regions using MATLAB
  • Explore the concept of changing the order of integration in multiple integrals
  • Investigate the implications of different bounds on the evaluation of integrals
USEFUL FOR

Students and educators in mathematics, particularly those studying calculus, as well as professionals working with multivariable integrals and geometric interpretations in engineering or physics.

TheSodesa
Messages
224
Reaction score
7

Homework Statement



Let ##T \subset R^3## be a set delimited by the coordinate planes and the surfaces ##y = \sqrt{x}## and ##z = 1-y## in the first octant.

Write the intgeral
<br /> \iiint_T f(x,y,z)dV<br />
as iterated integrals in at least 3 different ways.

Homework Equations



<br /> \iiint_T f(x,y,z)dV = \int_a^b \int_{y_1 (x)}^{y_2 (x)} \int_{z_1 (x,y)}^{z_2 (x,y)} f(x,y,z) dx dy dz<br />

The Attempt at a Solution



My interpretation of this problem is that they want me to "simply" find out the upper and lower bounds of integration for 3 different cases, since there is no specific function to integrate.

This is a bit difficult to explain, since I can't show you a picture of the volume because I can't seem to be able to draw the ##y = \sqrt{x}## correctly in Matlab using this code:

syms x y z

f(x,z) = sqrt(x);
g(x,y) = 1 - y;

hold on
xlabel('x')
ylabel('y')
zlabel('z')
axis equal

ezsurf(f,0:1);
ezsurf(g,0:1)

Anyways, I'm having trouble seeing what the upper bounds are for the innermost iteration, whichever way I try and integrate this thing. For example, if I were to integrate first with respect to y, then x and finally z, I would write:
<br /> \int_0^1 \int_{0}^{(-z+1)^2} \int_{0}^{?} f(x,y,z) dy dx dz<br />
Just looking at the horrible picture that I drew on paper (which kind of looks like a tetrahedron cut off by the ##\sqrt{x}##-surface) is not helping. Does anybody have any hints on where to start. My brain is telling me that ##?## should be a plane of some sort, but the fact that it's cut off by the ##\sqrt{x}## is really throwing me off.

EDIT: The shape is simple (as in x-, y- and z-simple) in all 3 dimensions, so I was able to print out the projections to the different coordinate planes:

y(x):

H5_4yx.JPG


z(y)

H5_4zy.JPG
x(z):

H5_4zx.JPG
 
Last edited:
Physics news on Phys.org
After thinking about this for a bit I think this might be the correct answer for the case ##dy dx dz##:
<br /> \int_0^1 \int_{0}^{(1-z)^2} \int_{\sqrt{x}}^{1} f(x,y,z) dy dx dz<br />
I'm saying this, because
\begin{cases}

y = \sqrt{x} \iff x = y^2\\
y+z = 1 \iff z = 1- \sqrt{x} \iff x = (1-z)^2
\end{cases}

How does this look?
 
Last edited:
Using the same logic as above for two other cases:

##dxdydz##:

\int_{0}^{1} \int_{0}^{1-z} \int_{0}^{y^2}f(x,y,z) dxdydz
and ##dzdxdy##:
\int_{0}^{1} \int_{0}^{y^2} \int_{0}^{1-y} f(x,y,z) dzdxdy
 
Last edited:

Similar threads

  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
Replies
4
Views
2K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
Replies
6
Views
2K