Problem 59 - Precalculus : Building Concepts and Connections

Question

Convert each of the given polar equations to rectangular form. $$r \cos \theta=4$$

Step-by-Step Solution

Answer

The rectangular form of the given polar equation is \(x = 4\).

Step 1: Identify the polar equation

The given polar equation is \(r \cos \theta=4\).

Step 2: Convert the polar equation to rectangular form

The relationship between polar and rectangular coordinates is \(x = r \cos \theta\) and \(y = r \sin \theta\). We see that the given polar equation can be mapped directly to the coordinate conversion equation: \(x = r \cos \theta\). Therefore, substituting \(r \cos \theta\) with \(x\), we get: \(x = 4\).

Key Concepts

Polar Coordinates

In mathematics, polar coordinates present an alternative to the traditional Cartesian or rectangular coordinate system for representing points on a two-dimensional plane. Unlike the rectangular system, which uses horizontal and vertical distances, polar coordinates define a point based on its distance from a reference point, called the pole (usually analogous to the origin in a rectangular system), and the angle between a reference direction and the line from the pole to the point.

Polar coordinates are denoted as \( (r, \theta) \), where \( r \) is the radial distance from the pole, and \( \theta \) is the angular component, typically measured in radians from the positive x-axis which acts as our reference direction. This system is particularly useful when dealing with problems that have a natural circular symmetry where angles and radii are more straightforward than x and y coordinates.

Rectangular Coordinates

On the flip side, rectangular coordinates work in a more familiar setting with a horizontal x-axis and a vertical y-axis, forming a grid where each point is specified by an x (horizontal) and y (vertical) value. Rectangular coordinates come in handy especially when working with linear equations, shapes with right angles, and in scenarios where horizontal and vertical measurements make more intuitive sense.

In rectangular coordinates, or the Cartesian plane, the location of a point is determined by \( (x, y) \), making it very visual and straightforward when plotting straight lines or parabolic curves. These coordinates are heavily used across various fields such as engineering, computer graphics, and navigation.

Coordinate Conversion

Transforming polar coordinates to rectangular coordinates, or vice versa, is known as coordinate conversion. This is an essential skill as it allows one to choose the most beneficial coordinate system for a given problem or to translate problems and solutions between systems when necessary.

The basic formulas for this conversion are centered around trigonometric relationships and Pythagorean theorem. For a point \( (r, \theta) \), to find the rectangular coordinates:\[ x = r \cos \theta \]\[ y = r \sin \theta \]
Conversely, to go from rectangular to polar, you can use:\[ r = \sqrt{x^2 + y^2} \]\[ \theta = \text{atan2}(y,x) \]
These formulas can be derived from the definitions of sine and cosine in a right triangle or by using the unit circle. A student should be comfortable with these conversions as they foster a more profound understanding of the relationship between the two coordinate systems.