Chapter 6: Problem 80
Use a graphing utility to graph and identify \(r=2+k \sin \theta\) for \(k=0,1,2,\) and \(3 .\)
Short Answer
Expert verified
The plots represent a series of cardioid shapes with one 'lobe'. The lobe becomes more pronounced as k increases, while the radius along the x-axis remains constant at 2
Step by step solution
01
Graph for k=0
Set \(k = 0\) in the given function \(r=2+k \sin \theta\). The function becomes \(r = 2+0 \sin \theta\) which simplifies to \(r = 2\). This is a circle with radius 2, centered at the origin.
02
Graph for k=1
Set \(k = 1\) in the function. The function becomes \(r = 2+ 1\sin \theta\), or \(r = 2+\sin \theta\). Plot this on your graphing utility and observe the change from the original graph.
03
Graph for k=2
With \(k = 2\), the function changes to \(r = 2+ 2\sin \theta\), or \(r = 2+2\sin \theta\). Plot this on your graphing utility and observe the change from the previous graphs.
04
Graph for k=3
Replacing \(k\) with 3 gives \(r = 2+ 3\sin \theta\). Plot this on your graphing utility and observe the change from the previous graphs.
05
Identification
By comparing the graphs, identify and note the effects of changing k values on the polar function. As the value of k increases, the 'lobe' on the positive y-axis becomes more pronounced. The radius of the section along the x-axis remains at 2.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Graphing Utility
A graphing utility is a powerful tool that helps us visualize mathematical equations and their transformations. Since polar equations can be a bit tricky to plot manually, using a graphing utility becomes essential. Polar graphs use a coordinate system where each point is determined by a distance from the pole (the origin) and an angle from the polar axis.
When using a graphing utility:
When using a graphing utility:
- You simply input the equation; it handles the plotting.
- It offers capabilities to adjust the angle increments for smoother graphs.
- You can zoom in or out to better see the effects and shape.
Effects of Parameters
The effects of parameters in an equation like \( r = 2 + k \sin \theta \) are crucial in shaping the graph. The parameter \( k \) in this function modulates the influence of the trigonometric part on the radius of the polar circle:
- When \( k = 0 \), there is no modulation from the sine function; resulting in a perfect circle with radius 2.
- Increasing \( k \) introduces variations caused by the \( \sin \theta \) term.
- A higher \( k \) value enhances the amplitude of these variations, creating more distinct shapes, like lobes.
Circle Equation
In polar coordinates, a circle can be represented in a simple form. The constant term in the equation \( r = 2 + k \sin \theta \) contributes to the circle's base size. For \( k = 0 \), the equation reduces to \( r = 2 \), representing a circle with a radius of 2 centered at the pole. This is akin to the Cartesian equation of a circle, such as \( x^2 + y^2 = r^2 \).
However, adding a trigonometric component shifts or distorts the circle. Here, it leads to bulging on parts of the circle, creating a new shape depending on \( k \). Understanding this helps in identifying how circles and their derivatives appear in polar graphs.
However, adding a trigonometric component shifts or distorts the circle. Here, it leads to bulging on parts of the circle, creating a new shape depending on \( k \). Understanding this helps in identifying how circles and their derivatives appear in polar graphs.
Trigonometric Functions
Trigonometric functions, like sine and cosine, play a significant role in polar graphs. In our equation \( r = 2 + k \sin \theta \), \( \sin \theta \) affects the radial distance for different values of \( \theta \). It oscillates between -1 and 1, modulating the radius around the constant value.
- The sine component affects the position of the graph with respect to the polar axis.
- The behavior of \( \sin \theta \) at different \( \theta \) values helps create familiar polar shapes like cardioids or more complex inner loops.
- As \( k \) changes, it amplifies or reduces the impact of \( \sin \theta \), visually transforming the graph.