Chapter 11: Problem 10
Graph the following equations. $$ r=\frac{3}{2+\sin (\theta)} $$
Short Answer
Expert verified
The graph is a dimpled limaçon symmetric about the vertical axis.
Step by step solution
01
Identify the Equation Type
The polar equation given is in the form \( r = \frac{k}{a + b \sin(\theta)} \). This form represents a conic section, specifically a limaçon, which is a type of polar graph with distinctive loops or dimples depending on the parameters.
02
Determine ³¢¾±³¾²¹Ã§´Ç²Ô Characteristics
For the equation \( r = \frac{3}{2 + \sin(\theta)} \), we identify the constants: \( k = 3 \), \( a = 2 \), and \( b = 1 \). Since \( a > b \), the graph will be a dimpled limaçon without an inner loop.
03
Find Symmetry and Key Angles
Because the function has a \( \sin(\theta) \) component, the graph is symmetric about the vertical axis (θ = π/2). Evaluate the equation at key angles: \( \theta = 0, \frac{\pi}{2}, \pi, \frac{3\pi}{2} \) to understand the graph's key distances from the origin.
04
Calculate Polar Coordinates
Use the polar equation to calculate specific points:- \( \theta = 0 \): \( r = \frac{3}{2 + 0} = \frac{3}{2} \)- \( \theta = \frac{\pi}{2} \): \( r = \frac{3}{2 + 1} = 1 \)- \( \theta = \pi \): \( r = \frac{3}{2 - 0} = \frac{3}{2} \)- \( \theta = \frac{3\pi}{2} \): \( r = \frac{3}{2 - 1} = 3 \)
05
Plot the Graph
Using the calculated points, plot them in polar coordinates. Join the points smoothly to reflect the dimpled characteristic of the limaçon. The graph will have a larger radius at \( \theta = \frac{3\pi}{2} \) and symmetric dimpled shape about the vertical axis.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
³¢¾±³¾²¹Ã§´Ç²Ô
A limaçon is a fascinating type of graph in polar coordinates. It appears when you graph polar equations in the form \( r = \frac{k}{a + b \sin(\theta)} \) or \( r = \frac{k}{a + b \cos(\theta)} \). The shape of a limaçon can vary widely:
- It can have a loop (when \( b > a \))
- Be dimpled, resembling a heart-like shape (when \( a > b \))
- Or form a perfect circle in some cases
Conic Sections
Conic sections are shapes created by slicing a cone with a plane. The most common conic sections include circles, ellipses, parabolas, and hyperbolas. In polar coordinates, these sections appear when equations take specific forms, predicting beautiful and varied shapes.
- Circles have the simplest form.
- Ellipses are stretched circles.
- Parabolas open in one direction.
- Hyperbolas open in two directions.
Graphing Polar Equations
Graphing polar equations starts with converting equations into polar form, like our given equation \( r = \frac{3}{2 + \sin(\theta)} \). Polar graphs are plotted using angles \( \theta \) and radius \( r \).
- Identify the form: Check if it's a known shape like a limaçon.
- Analyze the constants to determine the key graph characteristics.
- Calculate key points by substituting angles \( \theta \) to find corresponding \( r \) values.
Symmetry in Polar Graphs
Symmetry plays a critical role in understanding and sketching polar graphs effectively. It simplifies the graphing process, providing a balanced design.
- Analyze symmetry in our equation which involves \( \sin(\theta) \), implying vertical axis symmetry (along \( \theta = \frac{\pi}{2} \)).
- Symmetric properties reduce computation by confirming that behavior on one side reflects that of another.
- This helps in rapidly plotting and checking your graph shape.