Chapter 11: Problem 3
Change the following from cylindrical to Cartesian (rectangular) coordinates. (a) \((6, \pi / 6,-2)\) (b) \((4,4 \pi / 3,-8)\)
Short Answer
Expert verified
(a) \((3\sqrt{3}, 3, -2)\); (b) \((-2, -2\sqrt{3}, -8)\).
Step by step solution
01
Understanding the Relationship between Coordinates
In cylindrical coordinates, a point in space is represented as \((r, \theta, z)\), where \(r\) is the radial distance from the \(z\)-axis, \(\theta\) is the angular position measured from the positive \(x\)-axis, and \(z\) is the height above the \(xy\)-plane.In Cartesian coordinates, a point is given as \((x, y, z)\). The conversion formulas from cylindrical to Cartesian coordinates are:\[x = r \cos \theta, \quad y = r \sin \theta, \quad z = z.\]
02
Convert Part (a) from Cylindrical to Cartesian Coordinates
Given cylindrical coordinates \((6, \pi / 6, -2)\):- Calculate \(x\): \[x = 6 \cos \left(\frac{\pi}{6}\right) = 6 \times \frac{\sqrt{3}}{2} = 3 \sqrt{3}. \]- Calculate \(y\): \[y = 6 \sin \left(\frac{\pi}{6}\right) = 6 \times \frac{1}{2} = 3. \]- The \(z\) coordinate remains the same as \(z = -2\).Thus, the Cartesian coordinates are \((3 \sqrt{3}, 3, -2)\).
03
Convert Part (b) from Cylindrical to Cartesian Coordinates
Given cylindrical coordinates \((4, 4\pi / 3, -8)\):- Calculate \(x\): \[x = 4 \cos \left(\frac{4\pi}{3}\right) = 4 \times \left(-\frac{1}{2}\right) = -2. \]- Calculate \(y\): \[y = 4 \sin \left(\frac{4\pi}{3}\right) = 4 \times \left(-\frac{\sqrt{3}}{2}\right) = -2\sqrt{3}. \]- The \(z\) coordinate remains the same as \(z = -8\).Thus, the Cartesian coordinates are \((-2, -2\sqrt{3}, -8)\).
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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 a way to describe the position of a point in a three-dimensional space using three parameters: \(r\), \(\theta\), and \(z\). This system is particularly useful when dealing with problems that have a natural circular symmetry, such as those encountered in physics and engineering.
- \(r\) represents the radial distance from the \(z\)-axis to the point. It's similar to the radius of a circle.
- \(\theta\) is the angular position. It is measured in radians and represents the angle from the positive \(x\)-axis on the \(xy\)-plane.
- \(z\) is the height of the point above the \(xy\)-plane, similar to the \(z\) in Cartesian coordinates.
Cartesian Coordinates
In contrast to cylindrical coordinates, Cartesian or rectangular coordinates describe a point using a straightforward grid system. Here, each point is given as \(x\), \(y\), \(z\), akin to a classic map or graph. This system is simple and intuitive, making it a popular choice for many mathematical applications.
- \(x\) is the horizontal position along the \(x\)-axis.
- \(y\) is the vertical position along the \(y\)-axis.
- \(z\) denotes the position along the \(z\)-axis, indicating height or depth.
Conversion Formulas
To convert between cylindrical and Cartesian coordinates, one must use a set of conversion formulas. These formulas translate the radial and angular components into the familiar rectangular coordinate system.
- The formula for \(x\) is \(*x = r \cos \theta*\). This relates the radial distance and angle to the horizontal position.
- For \(y\), use \(*y = r \sin \theta*\), which converts radial distance and angle to vertical position.
- The \(z\) coordinate remains unchanged, as both cylindrical and Cartesian systems share the same height dimension.
Trigonometric Functions
Trigonometric functions play a crucial role in the conversion process between cylindrical and Cartesian coordinates. These functions help in computing the necessary translations of angles and distances.
- **Cosine (\(\cos\))** is used when translating angles into an \(x\) component. It's part of the conversion formula for \(x\) as \(x = r \cos \theta\).
- **Sine (\(\sin\))** relates angles to a \(y\) component, appearing in the formula \(y = r \sin \theta\).
- These functions operate based on a right-angled triangle, making them extremely efficient at calculating dimensions for circular movements.