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Consider the pyramid with the base in the \(x y\) -plane of \([-2,2] \times[-2,2]\) and the vertex at the point \((0,0,8) .\) a. Show that the equations of the planes of the lateral faces of the pyramid are \(4 y+z=8\) \(4 y-z=-8, 4 x+z=8,\) and \(-4 x+z=8\) b. Find the volume of the pyramid.

Short Answer

Expert verified
Lateral face equations: \(4y+z=8\), \(4y-z=-8\), \(4x+z=8\), \(-4x+z=8\). Volume: \(\frac{128}{3}\).

Step by step solution

01

Understanding the Pyramid

The base of the pyramid is a square in the XY-plane spanning from \([-2, 2] \times [-2, 2]\). The vertex of the pyramid is located at \((0, 0, 8)\). We have to find the equations of the planes defining the lateral faces.
02

Equation of Plane 1

Consider the line from the vertex \((0, 0, 8)\) to one vertex of the base, such as \((-2, 2, 0)\). The equation is derived from the direction vector and position vector. Solving, we get: \(4y + z = 8\).
03

Equation of Plane 2

Using \((0, 0, 8)\) and another base vertex \((2, 2, 0)\), find the plane equation. This gives us: \(4x + z = 8\).
04

Equation of Plane 3

Next, consider \((0, 0, 8)\) to \((2, -2, 0)\). The equation for this plane is: \(4y - z = -8\).
05

Equation of Plane 4

Finally, for the vertex \((-2, -2, 0)\) and \((0, 0, 8)\), obtain: \(-4x + z = 8\).
06

Volume of the Pyramid Formula

The formula for the volume of a pyramid is \( V = \frac{1}{3} \text{Base Area} \times \text{Height} \).
07

Calculate Base Area

The base is a square with sides of length 4, so the area is \(4 \times 4 = 16\).
08

Calculate Height

The height of the pyramid is the distance from the base plane to the vertex, which is 8.
09

Calculate Volume

Substitute the base area and height into the volume formula: \( V = \frac{1}{3} \times 16 \times 8 = \frac{128}{3} \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Lateral Face Equations
When we consider a pyramid in a three-dimensional space, the lateral faces are the triangular sides that rise from the base to the apex or vertex. In this pyramid, the vertex is positioned at the point \((0, 0, 8)\). To determine the equations of these lateral faces, we need to consider the line that stretches from this vertex to each corner of the square base.To start off, let's look at the first lateral face, which connects the vertex \((0, 0, 8)\) with a base point such as \((-2, 2, 0)\). We derive the plane's equation by using the direction and position vectors, leading to the equation:- \(4y + z = 8\)For the second lateral face, consider the vertex with the base point \((2, 2, 0)\). Solving similarly, this gives us:- \(4x + z = 8\)Next, calculate for the line from \((0, 0, 8)\) to \((2, -2, 0)\), resulting in:- \(4y - z = -8\)Finally, for the line from \((-2, -2, 0)\) to the vertex, the equation becomes:- \(-4x + z = 8\)These equations describe the planes of each lateral face neatly. Understanding these faces requires both visualization and calculation of vectors within three dimensions.
Base Area Calculation
The base of our pyramid is square in shape, positioned symmetrically around the origin in the XY-plane. To find its area, we notice that it spans from \([-2, 2]\) for both the x and y coordinates.The sides of this square base measure 4 units each, calculated as the difference between the coordinates on either axis.- Each side length is 4 because spanning from \(-2\) to \(2\) is a 4-unit length segment.To calculate the area of the square base, simply multiply the length of one side by itself:- Base Area = Side \(\times\) Side- Base Area = \(4 \times 4 = 16\)Therefore, the area of the base is \(16\) square units. This area is crucial when it comes to calculating the volume, as it forms part of the formula for the volume of a pyramid.
Pyramid Height
In our geometric problem, the height of the pyramid is critical because it represents the perpendicular distance from the base plane to the vertex. In this specific configuration, the vertex is at the point \((0, 0, 8)\), while the base lies on the XY-plane.Since the base is located exactly on the XY-plane, the z-coordinate of \(0\) makes it simple to identify the height.- Simply look at the vertex's z-coordinate, which is \(8\).- The perpendicular height of the pyramid is, therefore, \(8\) units.This height, combined with the base area identified earlier, feeds directly into calculating the pyramid's volume using the formula:- \( V = \frac{1}{3} \times \, \text{Base Area} \times \, \text{Height} \)With both base area and height identified clearly, you can now easily compute the pyramid's volume.

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Most popular questions from this chapter

The following problems examine Mount Holly in the state of Michigan. Mount Holly is a landfill that was converted into a ski resort. The shape of Mount Holly can be approximated by a right circular cone of height 1100 ft and radius 6000 \(\mathrm{ft.}\) If the compacted trash used to build Mount Holly on average has a density 400 \(\mathrm{lb} / \mathrm{ft}^{3}\) , find the amount of work required to build the mountain.

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Consider a lamina occupying the region \(R\) and having the density function \(\rho\) given in the preceding group of exercises. Use a computer algebra system (CAS) to answer the following questions. a. Find the moments \(M_{x}\) and \(M_{y}\) about the \(x\) -axis and \(y\) -axis, respectively. b. Calculate and plot the center of mass of the lamina. c. [T] Use a CAS to locate the center of mass on the graph of \(R .\) [T] \(R\) is the trapezoidal region determined by the lines \(\quad y=0, y=1, y=x, \quad\) and \(y=-x+3 ; \rho(x, y)=2 x+y\)

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