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For the following exercises, describe the graph of each polar equation. Confirm each description by converting into a rectangular equation. $$r=\sec \theta$$

Short Answer

Expert verified
The graph is a vertical line at \( x = 1 \).

Step by step solution

01

Understand the Polar Equation

The given polar equation is \( r = \sec \theta \). In polar coordinates, \( r \) represents the radial distance from the origin, and \( \theta \) represents the angle measured counterclockwise from the positive x-axis. The secant function is the reciprocal of the cosine function, which means \( \sec \theta = \frac{1}{\cos \theta} \).
02

Express r in Terms of Trigonometric Functions

Let us express \( r \) using cosine: \( r = \frac{1}{\cos \theta} \). This can be rewritten as \( r \cos \theta = 1 \).
03

Convert to Rectangular Coordinates

In polar coordinates, \( x = r \cos \theta \) and \( y = r \sin \theta \). From Step 2, we have \( r \cos \theta = 1 \), which in rectangular coordinates becomes \( x = 1 \).
04

Interpret the Rectangular Equation

The equation \( x = 1 \) is a vertical line in the Cartesian coordinate plane. This means the polar equation \( r = \sec \theta \) describes a vertical line at \( x = 1 \).
05

Graph the Polar Equation

The graph of the polar equation \( r = \sec \theta \) will be a vertical line where each point on the line has an x-coordinate of 1. This confirms the conversion to rectangular coordinates, as any point on the line at \( x = 1 \) satisfies the original polar equation.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Rectangular Coordinates
Rectangular coordinates, also known as Cartesian coordinates, are a straightforward way to pinpoint any location in a plane. They're defined by two numbers:
  • \( x \): the horizontal position on the plane.
  • \( y \): the vertical position on the plane.
Together, these coordinates are represented as \((x, y)\). Each point in a two-dimensional space falls exactly at one unique pair of these values. A simple way to visualize this is by picturing a grid where each intersection has a specific \( x \) and \( y \) value. In the exercise, converting the polar equation to the rectangular equation resulted in the
expression \( x = 1 \). This describes a vertical line on the Cartesian plane, where every point has an \( x \)-coordinate of 1 regardless of the \( y \)-value.
Polar Equations
Polar equations provide a unique way to describe curves in a plane through radial distance and angular measurement. The polar coordinates are determined by:
  • \( r \): the radial distance from the origin.
  • \( \theta \): the angle from the positive x-axis.
These equations may initially appear complex but offer a powerful means to encode intricate curves, such as spirals and circles, using functional equations. The polar equation \( r = \sec \theta \) translates the relationship in terms of the angle, where the radial distance changes as the angle changes. Each point on the curve is defined by an \( r \)-\( \theta \) pair, providing a different perspective from the standard Cartesian method.
Trigonometric Functions
Trigonometric functions are crucial when working with polar coordinates as they connect angle measurements with distances, simplifying various mathematical conversions.
  • \( \cos \theta \): relates the adjacent side over hypotenuse in a right triangle.
  • \( \sec \theta \): is the reciprocal of \( \cos \theta \), so \( \sec \theta = \frac{1}{\cos \theta} \).
These relationships are pivotal in converting polar equations to rectangular equations. In this context, expressing \( r = \sec \theta \) as \( r \cos \theta = 1 \) simplifies the process, bridging the gap between the polar and rectangular coordinate systems, ultimately leading to the rectangular equation \( x = 1 \). This reveals the much easier-to-interpret line when viewed through Cartesian geometry.
Graphing
Graphing is a fundamental tool to visualize equations, be they in polar or rectangular form. For effective graphing:
  • Understand the equations you want to plot.
  • Determine whether to plot in polar coordinates (curves, circles) or Cartesian coordinates (straight lines, simple parabolas).
Polar graphs can look markedly different from their rectangular counterparts, offering a unique peek into the behavior of equations as you adjust \( \theta \). In this exercise, the graph of \( r = \sec \theta \) equates to a vertical line \( x = 1 \) in the rectangular coordinate system, showcasing uniform distance from the y-axis and consistent \( x \)-values. Mastering the transition and graphing ensures a deeper grasp of how mathematical representations interconnect.

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