Chapter 29: Problem 35
Perform the indicated operations involving cylindrical coordinates. Describe the surface for which the cylindrical coordinate equation is (a) \(r=2,(\mathrm{b}) \theta=2,(\mathrm{c}) z=2\)
Short Answer
Expert verified
(a) Infinite vertical cylinder, (b) Half-plane at 2 radians, (c) Plane at height 2.
Step by step solution
01
Understand Cylindrical Coordinates
Cylindrical coordinates consist of three components: * \( r \): the radial distance from the z-axis.* \( \theta \): the angle in the \(xy\)-plane from the positive \(x\)-axis.* \( z \): the height above or below the \(xy\)-plane.
02
Describe the Surface for \( r = 2 \)
In cylindrical coordinates, fixing \( r = 2 \) implies a circular cylinder centered around the \( z \)-axis with a radius of 2. This means for every \( (x,y) \), \( x^2 + y^2 = 4 \). The height \( z \) can be any value, so the surface is an infinite vertical cylinder along the \(z\)-axis.
03
Describe the Surface for \( \theta = 2 \)
Fixing \( \theta = 2 \) means all points make an angle of 2 radians with the positive \(x\)-axis. This arises as a half-plane extending in the \(z\)-direction, where the points lie in a plane that slices through the \(z\)-axis at a specific angle (2 radians) with respect to the positive \(x\)-axis.
04
Describe the Surface for \( z = 2 \)
Fixing \( z = 2 \) creates a plane parallel to the \(xy\)-plane, but located at a height \( z = 2 \). This surface is infinite in the \(xy\)-direction and has no dependency on variants in \(r\) and \( \theta \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Circular Cylinder
A circular cylinder in cylindrical coordinates is an intriguing geometrical concept. When we talk about a circular cylinder, we imagine an infinite three-dimensional shape that wraps symmetrically around an axis, much like a soup can. In the context of cylindrical coordinates:
- "Circular" signifies that the cross-section intersecting this cylinder at any height is a circle.
- "Cylinder" refers to its constant radius and its continuity along a linear axis, typically the z-axis.
Coordinate Plane
The coordinate plane in the context of cylindrical coordinates plays a pivotal role in understanding how points are organized spatially. Generally, a coordinate plane is a two-dimensional flat surface formed by intersecting the x and y axes at a right angle, also known as the \( xy \)-plane.
In cylindrical coordinates, the surface being described when fixing a certain variable, such as \( z \), results in variation or intersection with a plane:
In cylindrical coordinates, the surface being described when fixing a certain variable, such as \( z \), results in variation or intersection with a plane:
- For \( z = 2 \), the plane moves parallel to the \( xy \)-plane and sits at the height of 2 units, forming a horizontal surface.
- This plane is infinite in the directions perpendicular to the z-axis, stretching along the x and y directions.
Radial Distance
The radial distance in cylindrical coordinates is a fundamental aspect that denotes the length from the z-axis to any point in the plane.
This is represented by the term \( r \) in the equations:
This is represented by the term \( r \) in the equations:
- It's similar to the radius of a circle, indicating how far away a point is from the center axis.
- By fixing \( r \), such as stating \( r = 2 \), a fixed circle is described in the \( xy \)-plane.
- Alterations in \( r \) affect how points are perceived within the circular plane, impacting the entire shape or figure associated with the value.
Angles in Mathematics
Angles in mathematics serve as a critical foundation for plotting points and describing surfaces within the coordinate system.
- In cylindrical coordinates, \( \theta \) describes the angle made with the positive x-axis in the \( xy \)-plane.
- This angular measurement determines direction, a concept used to represent line orientation or plane orientation within a multidimensional space.
- For example, an angle \( \theta = 2 \) implies that all points form a line making a 2 radian angle with the positive x-axis, often equating to creating a half-plane extending through the z-axis.