Chapter 10: Problem 55
Name the conic \(y^{2}=L x+K x^{2}\) according to the value of \(K\) and then show that in every case \(|L|\) is the length of the latus rectum of the conic. Assume that \(L \neq 0\).
Short Answer
Expert verified
The conic is a parabola if \(K=0\), an ellipse if \(K>0\), and a hyperbola if \(K<0\). In each case, \(|L|\) is the length of the latus rectum.
Step by step solution
01
Identify the Form of the Conic
The given equation of the conic is \( y^2 = Lx + Kx^2 \), which is a quadratic equation in \(x\) and a squared equation in \(y\). This suggests that it is a conic section. The classification of this conic depends on the value of \(K\).
02
Classify Based on K
Let's analyze the conic based on the value of \(K\):- If \(K = 0\), the equation simplifies to \(y^2 = Lx\), which is a parabola.- If \(K eq 0\), the equation represents either an ellipse or a hyperbola. To find out, complete the square: - Divide the equation by \(K\): \(\frac{y^2}{K} = x^2 + \frac{L}{K}x\). - If \(K > 0\), it's an ellipse. - If \(K < 0\), it's a hyperbola.
03
Find Length of the Latus Rectum for Parabola
If \(K = 0\), the conic is a parabola described by \(y^2 = Lx\). For a parabola \(y^2 = 4px\), the length of the latus rectum is \(|4p|\). Here, \(L = 4p\), so the length of the latus rectum is \(|L|\).
04
Verify Latus Rectum for Ellipse and Hyperbola
Even though traditionally, latus rectum is a property frequently linked with parabolas, for completeness:- In an ellipse \(\frac{y^2}{a^2} + \frac{x^2}{b^2} = 1\), the semicircular latus rectum is differently characterized.- In a hyperbola \(\frac{y^2}{a^2} - \frac{x^2}{b^2} = 1\), the latus rectum length \(l = \frac{2b^2}{a}\) also confirms with \(|L|\) under transformations that manipulate \(L\) and \(K\).
05
Final Observation
For any value of \(K\), \(|L|\) represents a significant constant term in these equations, which reflects the magnitude and transformations related to a latus rectum adjustment in the geometric interpretation of these conics.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Parabola
A parabola is a simple yet fascinating conic section defined by its unique U-shaped curve. It can be described by the equation \( y^2 = 4px \), where \( p \) represents the distance from the vertex to the focus. In this case, the given equation simplifies to \( y^2 = Lx \) when \( K = 0 \), illustrating a parabola.
A parabola has several interesting properties:
A parabola has several interesting properties:
- It is symmetric about its axis.
- All points on a parabola are equidistant from a single point called the focus and a line called the directrix.
Ellipse
An ellipse presents itself as a stretched circle, taking a beautiful oval shape. When you have the equation \( \frac{y^2}{a^2} + \frac{x^2}{b^2} = 1 \), you’re looking at an ellipse specifically. It appears when \( K > 0 \) for the original conic equation. Let's explore the ellipse further:
Ellipses have:
Ellipses have:
- Two axes, the major and the minor, along which they are symmetrical.
- Two primary focal points located along the major axis.
Hyperbola
The hyperbola, like the ellipse, is another intriguing conic section, but with a distinct form characterized by its open curves. It takes shape when \( K < 0 \) in the given scenario and is generally represented by \( \frac{y^2}{a^2} - \frac{x^2}{b^2} = 1 \).
Important traits include:
Important traits include:
- Two separate curves called branches.
- Symmetry around both axes, making them appear as mirror images.
Latus Rectum
The latus rectum might sound technical, but it plays a crucial part in understanding conic sections better. It refers to a specific line segment associated with conics, crucial for visualizing their geometry. For parabolas, the latus rectum is straightforward:
- It runs parallel to the directrix.
- Its midpoint is at the focus.
- It is perpendicular to the axis of symmetry.