Find a Cartesian equation for the curve. r = 9 cos(0)

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
Question
**Problem Statement:**

Find a Cartesian equation for the curve.

\[ r = 9 \cos(\theta) \]

**Explanation:**

The provided equation is in polar form, where \( r \) represents the radial distance from the origin, and \( \theta \) is the angle from the positive x-axis. The goal is to convert this equation into Cartesian coordinates (x, y).

**Conversion Steps:**

1. Recall the polar to Cartesian coordinate transformations:
   - \( x = r \cos(\theta) \)
   - \( y = r \sin(\theta) \)
   - \( r^2 = x^2 + y^2 \)

2. From the given equation \( r = 9 \cos(\theta) \), multiply both sides by \( r \):
   \[ r^2 = 9r \cos(\theta) \]

3. Substitute the Cartesian transformations:
   - Replace \( r^2 \) with \( x^2 + y^2 \)
   - Replace \( r \cos(\theta) \) with \( x \)

   This yields:
   \[ x^2 + y^2 = 9x \]

4. Rearrange the equation:
   \[ x^2 - 9x + y^2 = 0 \]

This is the Cartesian equation for the given polar curve.

**Diagram:**

The diagram contains a blank rectangular box, which likely serves as a placeholder for graphing the polar or Cartesian equation. The graph of the equation in polar coordinates \( r = 9 \cos(\theta) \) typically represents a circle centered at \( (4.5, 0) \) with a radius of 4.5 in Cartesian coordinates.
Transcribed Image Text:**Problem Statement:** Find a Cartesian equation for the curve. \[ r = 9 \cos(\theta) \] **Explanation:** The provided equation is in polar form, where \( r \) represents the radial distance from the origin, and \( \theta \) is the angle from the positive x-axis. The goal is to convert this equation into Cartesian coordinates (x, y). **Conversion Steps:** 1. Recall the polar to Cartesian coordinate transformations: - \( x = r \cos(\theta) \) - \( y = r \sin(\theta) \) - \( r^2 = x^2 + y^2 \) 2. From the given equation \( r = 9 \cos(\theta) \), multiply both sides by \( r \): \[ r^2 = 9r \cos(\theta) \] 3. Substitute the Cartesian transformations: - Replace \( r^2 \) with \( x^2 + y^2 \) - Replace \( r \cos(\theta) \) with \( x \) This yields: \[ x^2 + y^2 = 9x \] 4. Rearrange the equation: \[ x^2 - 9x + y^2 = 0 \] This is the Cartesian equation for the given polar curve. **Diagram:** The diagram contains a blank rectangular box, which likely serves as a placeholder for graphing the polar or Cartesian equation. The graph of the equation in polar coordinates \( r = 9 \cos(\theta) \) typically represents a circle centered at \( (4.5, 0) \) with a radius of 4.5 in Cartesian coordinates.
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