Chapter 12: Problem 17
In Exercises \(17-24\) , describe the sets of points in space whose coordinates satisfy the given inequalities or combinations of equations and inequalities. \begin{equation} \text {a. }x \geq 0, \quad y \geq 0, \quad z=0 \quad \text { b. } x \geq 0, \quad y \leq 0, \quad z=0 \end{equation}
Short Answer
Expert verified
a: First quadrant on XY-plane; b: Fourth quadrant on XY-plane.
Step by step solution
01
Understanding Inequality a
The inequalities for part (a) are \( x \geq 0 \), \( y \geq 0 \), and \( z = 0 \). This represents all the points in the \(xy\)-plane (where \(z = 0\)) that lie in the first quadrant. In the Cartesian coordinate system, this includes all points where the x-coordinate and y-coordinate are non-negative, and the z-coordinate is fixed at zero.
02
Plotting the Region for a
Visualize the XY-plane where \( z = 0 \). The inequality \( x \geq 0 \) means start from the y-axis to the right; \( y \geq 0 \) means start from the x-axis upwards. Together, these represent all points in the first quadrant of the XY-plane.
03
Describing the Set for a
The set is all points on or above the x-axis and to the right of the y-axis in the plane where \( z=0 \). Geometrically, it's the entire first quadrant of the XY-plane when projected onto the Z-axis.
04
Understanding Inequality b
The inequalities for part (b) are \( x \geq 0 \), \( y \leq 0 \), and \( z = 0 \). This represents all the points in the \(xy\)-plane that lie in the fourth quadrant. This plane represents all points in space where the x-coordinate is non-negative and the y-coordinate is non-positive.
05
Plotting the Region for b
Visualize again the XY-plane where \( z = 0 \). The inequality \( x \geq 0 \) still means include the positive x-values, but \( y \leq 0 \) means to include all values of y that are zero or negative. This defines the fourth quadrant.
06
Describing the Set for b
The set is all points on or below the x-axis and to the right side of the y-axis in the plane where \( z=0 \). Geometrically, it's the entire fourth quadrant of the XY-plane when projected onto the Z-axis.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Coordinate System
To understand points and shapes in three-dimensional space, we must grasp the concept of the coordinate system. The Cartesian coordinate system is the most common method to describe the position of a point using three coordinates: x, y, and z.
- The x-axis runs horizontally.
- The y-axis runs vertically.
- The z-axis adds depth, running front to back.
Inequalities in Geometry
Inequalities in geometry define a range of values that coordinates can take. In this context, an inequality specifies the regions in a space where points can exist.
When you see an inequality such as \( x \geq 0 \), it tells us that points are on or to the right of the y-z plane, while \( y \leq 0 \) indicates the points lie on or below the x-z plane.
When you see an inequality such as \( x \geq 0 \), it tells us that points are on or to the right of the y-z plane, while \( y \leq 0 \) indicates the points lie on or below the x-z plane.
- Inequalities like \( z = 0 \) specify an exact plane rather than a range.
- These inequalities help us define specific sections or regions in 3D space.
Quadrants in 3D Space
In three-dimensional space, quadrants become octants due to the addition of the z-axis. The xy-plane alone divides the space into four quadrants similar to the two-dimensional plane.
- The first quadrant in 2D is where both x and y are positive; in three dimensions, it extends into regions where x, y, and z values can create more complex combinations.
- For example, with \( z = 0 \), we look at a 2D slice of 3D space, simplifying the analysis to familiar 2D quadrants.
Cartesian Plane Visualization
Visualizing equations or inequalities on a Cartesian plane involves plotting them correctly to see the shape or area they describe. For equations like \( z = 0 \), visualization becomes about understanding a flat plane (XY) in three-dimensional space.
- Visualize the first quadrant by focusing on non-negative x and y.
- The fourth quadrant becomes clear when visualizing non-negative x and non-positive y.