Chapter 9: Problem 30
For the given polar equations: (a) identify the conic as either a parabola, an ellipse, or a hyperbola; (b) find the eccentricity and vertex (or vertices); and (c) graph. $$r=\frac{3}{3+8 \cos \theta}$$
Short Answer
Expert verified
The conic is a hyperbola with eccentricity \(\frac{8}{3}\), a vertex at \( (\frac{3}{11}, 0) \), and it opens outward from the pole.
Step by step solution
01
Identify the Type of Conic
The general form of a polar equation for a conic section is:\[ r = \frac{ed}{1 + e\cos(\theta)} \]where \(e\) is the eccentricity, and \(d\) is the semi-latus rectum. Here, the equation is given as \( r = \frac{3}{3 + 8\cos\theta} \). We can re-write this as \( r = \frac{\frac{3}{3}}{1 + \frac{8}{3}\cos\theta} \). Therefore, the equation becomes \( r = \frac{1}{1 + \frac{8}{3}\cos\theta} \), and from this, we identify \(e = \frac{8}{3}\). Since \(e > 1\), the conic is a hyperbola.
02
Find Eccentricity and Semi-Latus Rectum
The eccentricity \(e\) has already been identified as \(\frac{8}{3}\). To find the semi-latus rectum \(d\), we analyze the equation form:\[ r = \frac{\frac{3}{3}}{1 + \frac{8}{3}\cos\theta} = \frac{1}{1 + \frac{8}{3}\cos\theta} \].Since the numerator of the transformed equation is 1, which is the \(ed\), we find that \(ed = 1\). Given \(e = \frac{8}{3}\), we solve for \(d\) as \(d = \frac{1}{e} = \frac{1}{\frac{8}{3}} = \frac{3}{8}\).
03
Find Vertices
The vertices of a hyperbola in polar coordinates can be found using the formula for the radial distance from the pole:- For the extbf{positive focus}, the vertex occurs at \( \theta = 0 \) (cosine term is maximal):\[ r_1 = \frac{1}{1 + \frac{8}{3}} = \frac{1}{\frac{11}{3}} = \frac{3}{11} \]- For the extbf{negative focus}, the vertex occurs at \( \theta = \pi \) (cosine term is minimal):\[ r_2 = \frac{1}{1 - \frac{8}{3}} \] Since the equation \( \frac{8}{3} \) makes the denominator negative, the approach highlights the vertex along the directrix.
04
Graph the Conic
The graph of the hyperbola is plotted against the polar axis. In this case:- The vertex at \( \theta = 0 \) is nearest to the pole and occurs at \( r = \frac{3}{11} \).- On graphing, since \(e > 1\), the shape opens outward along the coordinate corresponding to \( \theta = 0 \) and \(\theta = \pi\), with the center at the pole.Though difficult to draw precisely without software, this visualization confirms the features such as eccentricity and behavior along \(r\) as \(\theta\) changes.
Unlock Step-by-Step Solutions & Ace Your Exams!
-
Full Textbook Solutions
Get detailed explanations and key concepts
-
Unlimited Al creation
Al flashcards, explanations, exams and more...
-
Ads-free access
To over 500 millions flashcards
-
Money-back guarantee
We refund you if you fail your exam.
Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Conic Sections
Conic sections are curves that can be formed by the intersection of a plane and a cone. There are mainly three types of conic sections: parabolas, ellipses, and hyperbolas. Each type has its unique properties:
Knowing the classification of a conic section helps in understanding its geometric shape and its behavior when represented graphically.
- Parabolas have the property that all points are equidistant from a single point called the focus and a line called the directrix.
- Ellipses are oval-shaped curves where the sum of distances from any point on the ellipse to two fixed points (foci) is constant.
- Hyperbolas consist of two separate curves that are mirror images of each other; here, the difference in distances to the foci is constant.
Knowing the classification of a conic section helps in understanding its geometric shape and its behavior when represented graphically.
Eccentricity
Eccentricity is a number that uniquely defines the shape of a conic section. It is usually denoted by the letter 'e'. The value of eccentricity determines how 'stretched' or 'focused' the shape of the conic will be:
- If e = 0, the conic section is a circle.
- If 0 < e < 1, it is an ellipse.
- If e = 1, the conic section is a parabola.
- If e > 1, it is a hyperbola.
Hyperbola
A hyperbola is a specific type of conic section characterized by its two separate curves known as branches. These branches open either horizontally or vertically and are mirror images centered around the origin in a symmetric fashion.For hyperbolas defined in polar coordinates like in the exercise, the equation typically looks like:\[ r = \frac{ed}{1 + e\cos(\theta)} \]Where \(e\) is the eccentricity and \(d\) is the semi-latus rectum.In this problem, \( e = \frac{8}{3} \), which tells us that our hyperbola is oriented horizontally, with vertices calculated at certain polar angles such as at \(\theta = 0\) and \(\theta = \pi\). This definition helps determine the distance from the center to the vertices and enables graphing of the hyperbola's path.
Polar Coordinates
Polar coordinates are a two-dimensional coordinate system where a point is located by a distance from the origin and an angle from a reference direction. This system is particularly useful for describing conic sections because of its natural fit with circular and radial symmetry.In the polar coordinate system, the position of a point is expressed as \((r, \theta)\), where:
- \( r \) is the radial distance from the pole (origin).
- \( \theta \) is the angular coordinate, the angle from the polar axis.