Chapter 15: Problem 1
1-2 Plot the point whose cylindrical coordinates are given. Then find the rectangular coordinates of the point. $$ \begin{array}{ll}{\text { (a) }(4, \pi / 3,-2)} & {\text { (b) }(2,-\pi / 2,1)}\end{array} $$
Short Answer
Expert verified
(a) Rectangular: (2, 2√3, -2); (b) Rectangular: (0, -2, 1).
Step by step solution
01
Understand Cylindrical Coordinates
Cylindrical coordinates are represented as \((r, \theta, z)\), where \(r\) is the radial distance from the z-axis, \(\theta\) is the angle in the xy-plane from the positive x-axis, and \(z\) is the height along the z-axis.
02
Plot Cylindrical Coordinates (a)
For the point \((4, \pi / 3, -2)\):- The radial distance \(r = 4\) means the point is 4 units away from the z-axis.- The angle \(\theta = \pi / 3\) means the point is 60 degrees from the positive x-axis.- The height \(z = -2\) means the point is 2 units below the xy-plane.
03
Convert Point (a) to Rectangular Coordinates
Use the conversion formulas: \(x = r \cos \theta\), \(y = r \sin \theta\), and \(z = z\).- Calculate \(x = 4 \cos(\pi / 3) = 4 \times \frac{1}{2} = 2\).- Calculate \(y = 4 \sin(\pi / 3) = 4 \times \frac{\sqrt{3}}{2} = 2\sqrt{3}\).- Maintain \(z = -2\).- So, the rectangular coordinates are \((2, 2\sqrt{3}, -2)\).
04
Plot Cylindrical Coordinates (b)
For the point \((2, -\pi / 2, 1)\):- The radial distance \(r = 2\) means the point is 2 units away from the z-axis.- The angle \(\theta = -\pi / 2\) means the point is 90 degrees clockwise from the positive x-axis, landing on the negative y-axis.- The height \(z = 1\) means the point is 1 unit above the xy-plane.
05
Convert Point (b) to Rectangular Coordinates
Use the conversion formulas: \(x = r \cos \theta\), \(y = r \sin \theta\), and \(z = z\).- Calculate \(x = 2 \cos(-\pi / 2) = 2 \times 0 = 0\).- Calculate \(y = 2 \sin(-\pi / 2) = 2 \times (-1) = -2\).- Maintain \(z = 1\).- So, the rectangular coordinates are \((0, -2, 1)\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Cylindrical Coordinates
Cylindrical coordinates are an extension of 2D polar coordinates into a three-dimensional framework. These coordinates consist of three components:
- The radial distance \( r \), which measures how far the point is from the origin, projected onto the xy-plane.
- The angular coordinate \( \theta \), measured in radians, which is the angle formed with the positive x-axis.
- The height \( z \), which indicates the vertical distance of the point from the xy-plane.
Coordinate Conversion
Converting between cylindrical coordinates \((r, \theta, z)\) and rectangular coordinates \((x, y, z)\) helps in simplifying calculations and understanding geometry.**How to Convert Cylindrical to Rectangular Coordinates?**The formulas are straightforward:
- \( x = r \cos \theta \)
- \( y = r \sin \theta \)
- \( z = z \) remains the same as the height in both systems.
Plotting Points
Plotting points in cylindrical coordinates requires mapping radial, angular, and vertical aspects onto a 3D system. The process can seem daunting initially but becomes intuitive with practice.**Steps to Plot Cylindrical Points:**1. Start with the radial distance \( r \), moving straight out from the z-axis.2. Use the angle \( \theta \) to pivot around the z-axis, similar to drawing an angle in a polar plane.3. Finally, adjust the point vertically by the height \( z \), shifting upwards or downwards from the xy-plane.For instance, consider the point \((2, -\pi/2, 1)\):
- Move 2 units from the origin along the plane.
- Pivot -90 degrees clockwise, which lands you on the negative y-axis.
- Move up 1 unit, aligning with the \( z \)-value.