Chapter 10: Problem 39
Identify and graph each polar equation. $$ r=2+2 \cos \theta $$
Short Answer
Expert verified
Graph the ±ô¾±³¾²¹Ã§´Ç²Ô with an inner loop present at \( r = 2 + 2 \, \cos \theta \).
Step by step solution
01
Recognize the Standard Polar Form
Identify the given polar equation and recognize it as part of a standard form. The equation given is \[ r = 2 + 2 \, \cos \theta \]This is a polar equation that can be identified as a ±ô¾±³¾²¹Ã§´Ç²Ô.
02
Determine Key Characteristics
A ±ô¾±³¾²¹Ã§´Ç²Ô of the form \[ r = a + b \, \cos \theta \]The constants in the equation are: \[ a = 2 \, \text{and} \, b = 2 \]Since \[ a = b \]this specific ±ô¾±³¾²¹Ã§´Ç²Ô will have an inner loop.
03
Find Important Points
Find and plot the points for specific values of \( \theta \):For \( \theta = 0 \):\[ r = 2 + 2 \, \cos(0) = 4 \]For \( \theta = \frac{\pi}{2} \):\[ r = 2 + 2 \, \cos \left( \frac{\pi}{2} \right) = 2 \]For \( \theta = \pi \):\[ r = 2 + 2 \, \cos(\pi) = 0 \]For \( \theta = \frac{3\pi}{2} \):\[ r = 2 + 2 \, \cos \left( \frac{3\pi}{2} \right) = 2 \]
04
Sketch the Graph
Using the points calculated from Step 3, sketch the graph of the ±ô¾±³¾²¹Ã§´Ç²Ô. The plot should reflect the shape with an inner loop, starting at (4, 0) and going through (0, Ï€).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
±ô¾±³¾²¹Ã§´Ç²Ô
A ±ô¾±³¾²¹Ã§´Ç²Ô is a type of curve represented by polar equations of the form either \( r = a + b \, \text{cos} \, \theta \) or \( r = a + b \, \text{sin} \, \theta \). Limaçons have unique and interesting shapes that vary depending on the values of \( a \) and \( b \). In our case, \( r = 2 + 2 \, \text{cos} \, \theta \), the constants \( a \) and \( b \) both equal 2. Some key characteristics of ±ô¾±³¾²¹Ã§´Ç²Ôs include:
- If \( a < b \), the ±ô¾±³¾²¹Ã§´Ç²Ô has an inner loop.
- If \( a = b \), it's a special ±ô¾±³¾²¹Ã§´Ç²Ô with an inner loop.
- If \( a > b \), it appears without an inner loop.
graphing polar coordinates
Understanding polar coordinates is essential for graphing polar equations like the ±ô¾±³¾²¹Ã§´Ç²Ô. A polar coordinate system represents a point in the plane using the distance from the origin \( r \) and the angle \( \theta \) from the positive x-axis. Here’s a quick overview:
- The distance \( r \) measures how far away a point is from the origin (pole).
- The angle \( \theta \) measures the rotational offset from the positive x-axis (polar axis).
- Calculate \( r \) for several values of \( \theta \), like \( 0 \, \text{and} \, \frac{\text{Ï€}}{2}, \, \text{Ï€}, \, \frac{\text{3Ï€}}{2} \).
- Plot these points on the polar coordinate plane.
- Connect the points to visualize the ±ô¾±³¾²¹Ã§´Ç²Ô curve.
trigonometric functions
Trigonometric functions like \( \text{cos} \, \theta \) and \( \text{sin} \, \theta \) are fundamental to understanding polar equations. In our exercise, \( r = 2 + 2 \, \text{cos} \, \theta \), we rely on the cosine function to determine \( r \) for different \( \theta \) values. Let's break down their role:
- Cosine function \( \text{cos} \, \theta \) returns a value between -1 and 1.
- For \( \theta = 0 \), \( \text{cos} \, 0 = 1 \), effectively making \( r = 2 + 2 \times 1 = 4 \).
- For \( \theta = \frac{\text{Ï€}}{2} \), \( \text{cos} \, \frac{\text{Ï€}}{2} = 0 \), leading to \( r = 2 + 2 \times 0 = 2 \).
- For \( \theta = \text{Ï€} \), \( \text{cos} \, \text{Ï€} = -1 \), resulting in \( r = 2 + 2 \times -1 = 0 \).