Chapter 8: Problem 49
For the following exercises, find the polar equation of the conic with focus at the origin and the given eccentricity and directrix. Directrix: \(x=-\frac{1}{4} ; e=\frac{7}{2}\)
Short Answer
Expert verified
The polar equation is \( r = \frac{\frac{7}{8}}{1 + \frac{7}{2} \cos(\theta)} \).
Step by step solution
01
Identify the type of conic
The eccentricity value \(e = \frac{7}{2} > 1\) indicates that the conic is a hyperbola. If \(e > 1\), the conic is a hyperbola.
02
Understand the polar equation format for conics
In polar coordinates, the equation of a conic section with focus at the origin is given by: \( r = \frac{ed}{1 + e \cos(\theta)} \) for a directrix \(x = d\). Here, the conic is opening towards the left since \(\cos(\theta)\) is used and the directrix is \(x = -\frac{1}{4}\).
03
Transform the directrix
For the directrix \(x = -\frac{1}{4}\), we use \(d = \frac{1}{4}\) in our formula because the derivation formula for the polar conic involves using the absolute value of the directrix position, hence \(d = \left| -\frac{1}{4} \right| = \frac{1}{4}\).
04
Plug values into the formula
Using \(e = \frac{7}{2}\) and \(d = \frac{1}{4}\), substitute into the polar equation: \[ r = \frac{\frac{7}{2} \cdot \frac{1}{4}}{1 + \frac{7}{2} \cos(\theta)} \]
05
Simplify the polar equation
Simplify the expression:\[ r = \frac{\frac{7}{8}}{1 + \frac{7}{2} \cos(\theta)} \]Now, the polar equation of the hyperbola with the given parameters is:\[ r = \frac{7/8}{1 + \frac{7}{2} \cos(\theta)} \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Conic Sections
Conic sections are curves obtained by intersecting a plane with a double-napped cone. They are a fundamental concept in geometry and appear in various mathematical contexts. The primary types of conics are:
- Ellipse
- Parabola
- Hyperbola
Hyperbola
A hyperbola is one of the fundamental types of conic sections characterized by having two identical branches that mirror each other. In simple terms, a hyperbola is formed when a plane cuts through both nappes of a cone. The key features of a hyperbola include:
- Two separate curves called "branches."
- An eccentricity greater than 1, which distinguishes it from ellipses and parabolas.
- Asymptotes, which create a framework around which the branches form.
Eccentricity
Eccentricity is a crucial concept in defining and differentiating conic sections. It measures the deviation of a conic from being circular. The eccentricity (\(e\)) value depends on the type of conic section, acting as a determinant of its shape:
- \(e = 1\) for parabolas.
- \(e < 1\) for ellipses.
- \(e > 1\) for hyperbolas.
Directrix
The directrix is a fixed line used in the description of a conic section. It acts as a reference line along with the eccentricity to define the conic in polar coordinates. Here are some important points about the directrix:
- It is perpendicular to the axis of symmetry of the conic.
- In polar equations, conics use the directrix to represent distance and focus properties of the curve.
- The directrix helps determine the position and orientation of the conic.