Chapter 11: Problem 29
(a) Use the discriminant to identify the conic. (b) Confirm your answer by graphing the conic using a graphing device. $$2 x^{2}-4 x y+2 y^{2}-5 x-5=0$$
Short Answer
Expert verified
The conic is a parabola.
Step by step solution
01
Rewrite the Equation in Standard Form
The given equation is \(2x^2 - 4xy + 2y^2 - 5x - 5 = 0\). Note that it already resembles a conic equation with terms \(Ax^2 + Bxy + Cy^2 + Dx + Ey + F = 0\). Here, \(A = 2\), \(B = -4\), \(C = 2\).
02
Calculate the Discriminant
The discriminant for conic sections is calculated using the formula \( B^2 - 4AC \). Substitute the values we identified: \((-4)^2 - 4(2)(2) = 16 - 16 = 0\).
03
Identify the Conic Based on the Discriminant
If \( B^2 - 4AC = 0 \), the conic section is a parabola. Therefore, the given equation represents a parabola.
04
Graph the Conic Section
Using a graphing device, input the equation \(2x^2 - 4xy + 2y^2 - 5x - 5 = 0\). Observe the graph to check for a parabolic shape, confirming the result obtained using the discriminant.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Discriminant
The discriminant is a crucial tool in identifying the type of conic section represented by a quadratic equation in two variables. In standardized forms, these equations appear as \( Ax^2 + Bxy + Cy^2 + Dx + Ey + F = 0 \). The discriminant helps ascertain whether the equation outlines a parabola, ellipse, or hyperbola. This determinant is formulated as \( B^2 - 4AC \). Each conic type has a specific discriminant value:
- If \( B^2 - 4AC = 0 \), the conic is a parabola.
- If \( B^2 - 4AC > 0 \), it indicates a hyperbola.
- If \( B^2 - 4AC < 0 \), it reveals an ellipse.
Parabolas
Parabolas are one of the simplest forms of conic sections and have unique properties that distinguish them from ellipses and hyperbolas. A parabola occurs when a plane intersects a cone at an angle parallel to the side of the cone. This results in a U-shaped curve which can open either up, down, left, or right.Key characteristics of parabolas include:
- Vertex: the highest or lowest point on the parabola.
- Axis of symmetry: a line that evenly splits the parabola into two mirror-image halves.
- Focus and directrix: a parabola is defined as the set of points equidistant from a fixed point (the focus) and a line (the directrix).
Graphing Conics
Visualizing conic sections through graphing not only confirms analytic findings but also provides a clear picture of the specific nature and orientation of the curve. When graphing conics, it's important to utilize a graphing device or software that accurately displays these complex shapes.To graph our particular equation, \( 2x^2 - 4xy + 2y^2 - 5x - 5 = 0 \), using graphing technology involves several steps:
- Input the equation into a graphing calculator or software.
- Observe the plotted conic to check for characteristics—such as symmetry, focus, and directrix for parabolas.
- Confirm the results obtained from calculating the discriminant.