Chapter 8: Problem 67
Convert to a rectangular equation. $$r=5 \sec \theta$$
Short Answer
Expert verified
The rectangular equation is \( x = 5 \).
Step by step solution
01
Understand the given polar equation
The given polar equation is: \[ r = 5 \sec \theta \] This equation involves the polar coordinates where \( r \) is the radius and \( \theta \) is the angle.
02
Recall the definition of secant
Recall that \( \sec \theta \) is the reciprocal of \( \cos \theta \). So, \[ \sec \theta = \frac{1}{\cos \theta} \] We can rewrite the given equation to express \( r \) in terms of \( \cos \theta \) instead.
03
Substitute \( \sec \theta \)
Substitute \( \sec \theta \) with \( \frac{1}{\cos \theta} \). So the equation becomes: \[ r = \frac{5}{\cos \theta} \] Multiply both sides by \( \cos \theta \) to clear the fraction: \[ r \cos \theta = 5 \]
04
Use the polar-to-rectangular conversion formulas
Recall the polar-to-rectangular conversion formulas: \[ x = r \cos \theta \quad \text{and} \quad y = r \sin \theta \] From the equation obtained after Step 3, we have \( r \cos \theta = x \). Thus, \[ x = 5 \]
05
State the rectangular equation
The final rectangular equation, obtained from converting the given polar equation, is: \[ x = 5 \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polar Coordinates
Polar coordinates provide a way to locate a point in the plane using a radius and an angle rather than traditional \(x\) and \(y\) coordinates. In polar coordinates, each point is defined by two values:
- **\[r\]**: The distance from the origin to the point.
- **\[\theta\]**: The angle measured from the positive x-axis in a counter-clockwise direction.
Rectangular Coordinates
Rectangular, or Cartesian, coordinates are the most common way to describe a point in the plane. Here, each point is defined by two orthogonal values:
- **\[x\]**: The horizontal distance from the origin.
- **\[y\]**: The vertical distance from the origin.
- \[ x = r \cos \theta \]
- \[ y = r \sin \theta \]
Secant Function
The secant function, written as \[ \sec \theta \], is closely related to the cosine function. Specifically, it's the reciprocal of cosine:
- **\[\sec \theta = \frac{1}{\cos \theta} \]**