Question

In Exercises \(9-14,\) find an equation in cylindrical coordinates for the equation given in rectangular coordinates. $$ z=5 $$

Short answer

The equation in cylindrical coordinates is \(z = 5\).

Step-by-step solution

Understand the relation between cylindrical and rectangular coordinates

The relationship between cylindrical and rectangular coordinates is expressed as \(x = rcos(\theta)\), \(y = rsin(\theta)\), and \(z = z\). This specific exercise doesn't require knowledge of the first two equations since the original equation doesn't involve x or y, only z.

Transform the equation from rectangular to cylindrical coordinates

Given the equation is \(z = 5\), in cylindrical coordinates, the equation remains the same since z is not affected by the coordinate system change. Therefore, the equation in cylindrical coordinates is still \(z = 5\).

Key concepts

Rectangular to Cylindrical Coordinate Conversion

Understanding how to switch from rectangular to cylindrical coordinates is crucial for problem-solving in multiple dimensions. In rectangular coordinates, positions are described using three values (x, y, z), representing distances along orthogonal axes. To convert these to cylindrical coordinates (r, \theta, z), the horizontal position (x, y) is reimagined in polar format \textemdash where 'r' is the radius (or distance from the origin) and '\theta' is the angle made with the positive x-axis. The z-value remains unchanged. Here's the formula breakdown:

\begin{itemize}\t

For the r-coordinate: calculate the distance to the origin with \t\t\(r =\sqrt{x^2 + y^2}\).\t

\t

For the \theta-coordinate: determine the angle with \t\t\(\theta =\atan2(y, x)\).\t

\t

The z-coordinate is consistent across both systems: \t\t\(z = z\).\t

For the equation \(z=5\), since it's independent of the x and y coordinates, conversion is straightforward \textemdash no calculation for r or \theta is needed, and the cylindrical representation remains \(z = 5\).

Coordinate System Transformation

The transformation from one coordinate system to another involves changing the form of an equation or a point's coordinates to suit the new system's requirements. This is often done to simplify equations, exploit the symmetries of a system, or facilitate easier integration or differentiation. It's a form of representing the same physical reality but through a different mathematical lens.

In our exercise, the transformation from rectangular to cylindrical coordinates is relatively simple because the equation \(z=5\) only concerns the vertical dimension, which remains the same in both coordinate systems. However, transformations often require more complex operations, such as applying trigonometric relationships and considering the orientations of the axes. Throughout this process, it's important to preserve the physical meaning of the equations or points being transformed.

Equations in Multiple Coordinate Systems

Having the ability to work with equations in multiple coordinate systems opens up a world of possibilities for analyzing problems in mathematics and physics. Depending on the symmetry of a problem, certain coordinate systems might offer a more natural or simplified description. For example, spherical coordinates are often better suited for problems involving spherical symmetry, such as gravitational fields around planets. Rectangular coordinates, on the other hand, might be easier when dealing with problems that involve linear motion or rectangular boundaries.

In practice, knowing when and how to apply these alternative coordinate systems is a key part of a mathematician's or physicist's toolkit. When faced with an equation like \(z=5\), it's valuable to recognize that its simplicity in rectangular form carries over to cylindrical coordinates directly. However, for more complex equations, the process can involve substituting expressions for x, y, and z with their cylindrical or spherical counterparts, often leading to significant reworking of the equation.