Chapter 11: Problem 15
Find the parametric equations of the line through \((5,-3,4)\) that intersects the \(z\) -axis at a right angle.
Short Answer
Expert verified
Parametric equations: \(x = 5 + at, y = -3 + bt, z = 4\).
Step by step solution
01
Understand the Problem
We need to find parametric equations for a line that passes through the point \((5, -3, 4)\) and intersects the z-axis at a right angle.
02
Determine the Direction Vector
A line perpendicular to the z-axis will have a direction vector of the form \((a, b, 0)\) because the line must be parallel to the xy-plane.
03
Write the Parametric Equations
The parametric equations for a line through the point \((5, -3, 4)\) with direction vector \((a, b, 0)\) will be:\[x = 5 + at,\quad y = -3 + bt,\quad z = 4\]
04
Ensure Z-Axis Perpendicularity
Since the line must intersect the z-axis perpendicularly, the z-component of the direction vector is 0, which is already satisfied with direction vector \((a, b, 0)\).
05
Solution Verification
The line intersects the z-axis when \(x = 0\) and \(y = 0\), since we need the line to pass through the z-axis. However, it is sufficient that the direction vector only affects x and y to ensure perpendicularity to the z-axis, as z remains constant. Thus, our set of equations is valid.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Perpendicular Lines
When discussing lines in three-dimensional space, two lines are perpendicular if they meet at a right angle. A line that is perpendicular to the z-axis specifically has to lie entirely within a plane parallel to the xy-plane. This is because the z-axis is vertical, so any line that crosses it perpendicularly does so without moving up or down the z-values. The essence of ensuring a perpendicular intersection with the z-axis involves understanding that the only varying components of the line's direction would be along the x and y axes, leaving the z component fixed.
Direction Vector
The direction vector of a line is crucial as it defines the line's pathway through space. In our problem, we determined our direction vector to have the form \((a, b, 0)\). This choice results because a direction vector \((a, b, 0)\) ensures that the line runs parallel to the xy-plane and thus remains perpendicular to the z-axis.
- The x and y components \(a\) and \(b\) allow the line to move through different x and y coordinates.
- The z component being zero ensures perpendicularity, as there is no z direction displacement.
Z-Axis Intersection
For the line to intersect the z-axis, we usually think of it crossing the plane where the x and y coordinates are zero. However, for our specific problem, this constraint doesn't necessarily apply strictly; rather, we need the line's orientation to remain consistently aligned so it touches the z-axis at one fixed point along that axis. Consequently, the variation in x and y as defined by the parametric equations allows for looking at how these interact rather than directly demanding \(x = 0\) and \(y = 0\).
- The critical focus is on how the line's z value remains constant, thereby automatically ensuring an intersection with the z-axis at one point along its line.
- The direction is exclusively along the x and y path, which effectively addresses where the line covers as \(t\) changes.
Parametric Form in 3D
Parametric equations in 3D define a line using separate expressions for each coordinate as a function of a common parameter. Here, we use \(t\), with equations:
- \(x = 5 + at\)
- \(y = -3 + bt\)
- \(z = 4\)
- The starting point of the line is \((5, -3, 4)\), and \(t = 0\) will plug directly into this origin.
- As \(t\) shifts, it records how far we've moved from this initial point, controlled by our chosen direction vector.
- The equations provide the line's representation in clear numerical terms that describe both location and direction in 3D space.