Chapter 13: Problem 36
Find the volume of the solid trapped between the surface \(z=\cos x \cos y\) and the \(x y\) -plane, where \(-\pi \leq x \leq \pi\) \(-\pi \leq y \leq \pi\)
Short Answer
Expert verified
The volume is zero.
Step by step solution
01
Understand the Solid
The problem asks for the volume between the surface defined by \( z = \cos x \cos y \) and the \( xy \)-plane. This volume is defined over the domain \(-\pi \leq x \leq \pi\) and \(-\pi \leq y \leq \pi\).
02
Set Up the Double Integral for Volume
The volume \( V \) of the solid trapped between the surface \( z= \cos x \cos y \) and the \( xy \)-plane is given by the integral:\[V = \int_{-\pi}^{\pi} \int_{-\pi}^{\pi} \cos x \cos y \, dy \, dx\]This integral calculates the sum of infinitesimally small volumes \( \cos x \cos y \, dy \, dx \) over the defined domain.
03
Integrate with Respect to y
First, integrate \( \cos x \cos y \) with respect to \( y \):\[\int_{-\pi}^{\pi} \cos x \cos y \, dy = \cos x \left[ \sin y \right]_{y=-\pi}^{y=\pi}\]Calculate the limits:\( \cos x (\sin(\pi) - \sin(-\pi)) = \cos x (0 - 0) = 0 \).
04
Integrate with Respect to x
Since the integrand's integral with respect to \( y \) is zero, the next integral:\[\int_{-\pi}^{\pi} 0 \, dx = 0\]contributes nothing to the volume. Therefore, the total volume is zero over the domain.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Volume of a Solid
When we talk about the volume of a solid, we're referring to the total amount of space that a three-dimensional object occupies.
This is a fundamental concept in geometry and calculus, used extensively to solve real-world problems.
For a solid lying between a surface and a plane, the volume is found by integrating the height of the solid, given by the equation of the surface, over the area of the base.
This is a fundamental concept in geometry and calculus, used extensively to solve real-world problems.
For a solid lying between a surface and a plane, the volume is found by integrating the height of the solid, given by the equation of the surface, over the area of the base.
- In this exercise, the surface is given by the function \( z = \cos x \cos y \) and the base is the rectangular region \(-\pi \leq x \leq \pi\) and \(-\pi \leq y \leq \pi\).
The volume is computed using a double integral. - The double integral sums up infinitesimal volume elements \( \cos x \cos y \, dy \, dx \), with \( dy \, dx \) representing tiny areas on the base, and \( \cos x \cos y \) representing the height at each point of the base.
Surface Integral
Surface integrals extend the concept of integration to functions over surfaces.
In general, a surface integral computes the sum of a function over a particular surface, taking into account both the function's value and the shape of the surface.
In this exercise, while we're not directly performing a surface integral, the idea relates closely because the surface \( z = \cos x \cos y \) is integral to the problem.
In general, a surface integral computes the sum of a function over a particular surface, taking into account both the function's value and the shape of the surface.
In this exercise, while we're not directly performing a surface integral, the idea relates closely because the surface \( z = \cos x \cos y \) is integral to the problem.
- Essentially, the double integral used to find the volume is a kind of surface integral where the surface is the projection onto the \( xy \)-plane.
The value of the function \( z = \cos x \cos y \) over this surface provided the "height" of the surface above each point in the domain. - A classic surface integral problem might compute the flow of a vector field across a curved surface, whereas here we sum up volumes beneath the surface itself.
Integral Calculus
Integral calculus is a cornerstone in mathematics that deals with the accumulation of quantities.
Inevitably, it has a vast array of applications including calculating areas, volumes, and more.
In the case of the volume calculation for the given solid, we use a double integral, a tool from integral calculus.
Inevitably, it has a vast array of applications including calculating areas, volumes, and more.
In the case of the volume calculation for the given solid, we use a double integral, a tool from integral calculus.
- The double integral \( \int \int \) enables us to add up infinitely many infinitesimal quantities, such as small bits of area or volume, to find a total.
- In our example, each element \( \cos x \cos y \, dy \, dx \) is calculated by multiplying the function value at a point by a tiny area.
- This method of integration reflects one of the most potent ways integral calculus helps solve real-world problems, by approximating and then adding up small parts to understand a whole.