Chapter 8: Problem 7
Graph the polar equation \(r=1+2 \sin \theta\) for \(\theta \in[0,2 \pi]\).
Short Answer
Expert verified
Graph the equation \(r = 1 + 2 \sin \theta\) by plotting points and connecting them; the graph is a limacon with an inner loop.
Step by step solution
01
Understanding the Polar Equation
The given polar equation is \(r = 1 + 2 \sin \theta\). Here, \(r\) is the radius or the distance from the origin, and \(\theta\) is the angle measured counterclockwise from the positive x-axis. The goal is to graph this equation for \(\theta\) ranging from 0 to \(2\pi\).
02
Generate Coordinate Points
To graph this, generate a set of points by calculating \(r\) for various values of \(\theta\). Start by computing \(r\) for \(\theta = 0, \frac{\pi}{6}, \frac{\pi}{4}, \frac{\pi}{3}, \frac{\pi}{2}, \text{etc},\) up to \(2\pi\).
03
Calculate Sample Points
Here are some sample points: - For \(\theta = 0\), \(r = 1 + 2 \sin(0) = 1\) - For \(\theta = \frac{\pi}{2}\), \(r = 1 + 2 \sin(\frac{\pi}{2}) = 3\) - For \(\theta = \pi\), \(r = 1 + 2 \sin(\pi) = 1\) - For \(\theta = \frac{3\pi}{2}\), \(r = 1 + 2 \sin(\frac{3\pi}{2}) = -1\) - Continue this process for several more values including the intermediates.
04
Plot Points on Polar Grid
Plot all the calculated coordinate points using a polar grid. Each point is represented by its corresponding \(r\) and \(\theta\).
05
Draw the Graph
Connect the plotted points smoothly to form the graph. The shape obtained will be a limacon with an inner loop due to the negative value when \(\theta = \frac{3\pi}{2}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polar Coordinates
Polar coordinates offer a unique way to locate points in a plane using a radius and an angle. In this system, a point is specified by its distance from a reference point (usually the origin) and the angle from a reference direction (often the positive x-axis). The configuration follows:
- The radius, denoted by \(r\), represents the distance from the origin.
- The angle, denoted by \(\theta\), is measured counterclockwise from the positive x-axis.
Graphing Polar Equations
Graphing polar equations involves plotting points based on their radius \(r\) and angle \(\theta\). For example, consider the polar equation \(r = 1 + 2 \sin \theta\). Here are steps to graph this equation:
- Identify the function \(r\) in terms of \(\theta\).
- Generate coordinate points by calculating \(r\) for various angles from 0 to \(2\pi \).
- Plot these points on a polar grid where each point corresponds to its \(r\) and \(\theta\) values.
- Connect the points smoothly to visualize the curve.
Limacon
A limacon is a type of polar graph named after the French word for 'snail.' It is defined by polar equations of the form \(r = a + b \sin \theta\) or \(r = a + b \cos \theta\), where \(a\) and \(b\) are constants. Limacons can have various shapes depending on the values of \(a\) and \(b\):
- When \(a < b\), the limacon has an inner loop.
- When \(a = b\), it forms a cardioid shape.
- When \(a > b\), the limacon looks like a distorted circle.