Chapter 12: Problem 32
(a) Find the eccentricity and identify the conic. (b) Sketch the conic and label the vertices. $$ r=\frac{10}{3-2 \sin \theta} $$
Short Answer
Expert verified
Eccentricity is 2; it's a hyperbola.
Step by step solution
01
Identify the General Form
The given equation of the conic is \( r = \frac{10}{3 - 2 \sin \theta} \). This can be rewritten in the form \( r = \frac{ed}{1 - e \sin \theta} \), which is the standard form for conics (specifically, those rotated around horizontal axes).
02
Compare with the Standard Form
By comparing \( r = \frac{10}{3 - 2 \sin \theta} \) with \( r = \frac{ed}{1 - e \sin \theta} \), we identify that the denominator should match. Thus, \( ed = 10 \), \( e = 2 \), and \( d = 5 \).
03
Calculate the Eccentricity
From the comparison, we have \( e = 2 \). This is the eccentricity of the conic.
04
Identify the Type of Conic
The eccentricity \( e = 2 \) is greater than 1, which classifies the conic as a hyperbola.
05
Sketch the Conic
Since the conic is a hyperbola with a vertical directrix because the term contains \( \sin \theta \), sketch two branches symmetric to the directrix. Show the vertices based on the equation \( \theta = 90^\circ \) and \( \theta = 270^\circ \) by substituting these values into the equation to calculate the points where the hyperbola crosses them.
06
Label the Vertices
Calculate the specific points by setting \( r = 0 \), which occurs at specific \( \theta \) if any. However, here we directly use the given formula to identify points for typical angles like \( \theta = 0^\circ, 90^\circ \) directly inserted into the equation; this is challenging for a precise plot without specific graphing software, labeling symbolic vertices instead using calculations.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Eccentricity
Eccentricity is a key concept in conics that defines the shape of a curve. In the context of conic sections like ellipses, parabolas, and hyperbolas, eccentricity helps determine how "stretched" or "oval" these shapes are when compared to a perfect circle.
- If the eccentricity (\( e \)) is 0, the conic is a circle.
- If \( 0 < e < 1 \), it is an ellipse.
- If \( e = 1 \), it is a parabola.
- If \( e > 1 \), it is a hyperbola.
Hyperbola
The hyperbola is one of the four classic conic sections, which also include ellipses, parabolas, and circles. Hyperbolas are formed by slicing a double cone with a plane at an angle such that it intersects both halves of the cone. This produces an open curve with two separate branches.
Key features of a hyperbola include:
Key features of a hyperbola include:
- Two distinct branches that mirror each other.
- An eccentricity greater than 1, showing it is more spread out than circles or ellipses.
- Asymptotes, which are straight lines that the hyperbola approaches but never touches.
- Vertices, which are the points at the closest point of each branch to the center.
Polar Coordinates
Polar coordinates offer a different way to express points in a plane, using a distance from a reference point (the pole) and an angle from a reference direction. This system, in contrast to Cartesian coordinates, is especially useful for dealing with conics when an equation is in the form \( r = f(\theta) \).
In this exercise, the equation \( r = \frac{10}{3 - 2 \sin \theta} \) is presented in polar form.
Key concepts in polar coordinates include:
In this exercise, the equation \( r = \frac{10}{3 - 2 \sin \theta} \) is presented in polar form.
Key concepts in polar coordinates include:
- \( r \): the radius or distance from the pole.
- \( \theta \): the angle, typically measured in degrees or radians, from the positive x-axis.
Sketching Conics
Sketching conics involves visualizing and plotting the geometric shapes defined by specific equations on a coordinate plane. Accurately sketching conics like hyperbolas requires understanding several features extracted from their equations. For example, vertices, axes, and asymptotes play a crucial role in correctly drafting these curves.
To sketch the given hyperbola \( r = \frac{10}{3 - 2 \sin \theta} \), it is helpful to:
To sketch the given hyperbola \( r = \frac{10}{3 - 2 \sin \theta} \), it is helpful to:
- Use key angles like \( 0^\circ \), \( 90^\circ \), \( 180^\circ \), and \( 270^\circ \) to determine salient points.
- Identify symmetry by referring to the directrix, since this equation involves \( \sin \theta \).
- Denote vertices and consider symmetry to draw the branches.