Chapter 10: Problem 15
Use the discriminant to determine whether the graph of the equation is an ellipse (or a circle), a hyperbola, or a parabola. $$2 x^{2}-8 x y+7 y^{2}+x-2 y+1=0$$
Short Answer
Expert verified
The equation represents a hyperbola.
Step by step solution
01
Identify coefficients
Write the given equation in the standard quadratic form and identify the coefficients. The given equation is 2x^2-8xy+7y^2+x-2y+1=0 Here, we identify the coefficients as follows: A=2, B=-8, C=7.
02
Calculate the Discriminant
Use the formula for the discriminant of a conic section: D = B^2 - 4AC Plug in the values of A, B, and C: D = (-8)^2 - 4(2)(7) Calculate this expression to find the discriminant.
03
Simplify the Discriminant
Continue simplifying the discriminant: D = 64 - 56 = 8 So, the discriminant D is 8.
04
Determine the Type of Conic Section
Use the value of the discriminant to determine the type of conic section: - If D < 0, the conic is an ellipse (or a circle).- If D = 0, the conic is a parabola.- If D > 0, the conic is a hyperbola. Since D = 8 > 0, the conic section is a hyperbola.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Ellipse
An ellipse is a conic section that forms a closed curve, resembling an elongated circle. In terms of equations, it is defined as follows:
When the equation of the conic section has its discriminant (\text{D}) less than 0 (\text{D} < 0), it represents an ellipse or a circle.
The standard equation of an ellipse is \[ \frac{x^2}{a^2} + \frac{y^2}{b^2} = 1 \] Here, \text{a} and \text{b} are the lengths of the semi-major and semi-minor axes, respectively. Key features of an ellipse include:
When the equation of the conic section has its discriminant (\text{D}) less than 0 (\text{D} < 0), it represents an ellipse or a circle.
The standard equation of an ellipse is \[ \frac{x^2}{a^2} + \frac{y^2}{b^2} = 1 \] Here, \text{a} and \text{b} are the lengths of the semi-major and semi-minor axes, respectively. Key features of an ellipse include:
- Major Axis: The longest diameter of the ellipse, running through its center and both foci.
- Minor Axis: The shortest diameter, perpendicular to the major axis at the center.
- Foci (plural of focus): Two fixed points inside the ellipse such that the sum of the distances from any point on the ellipse to the foci is constant.
Hyperbola
A hyperbola is another type of conic section which is defined by its open, curve-like appearance. Unlike an ellipse, a hyperbola consists of two separate curves.
This is determined when the discriminant (\text{D}) of the conic section is greater than 0 (\text{D} > 0). The standard equation of a hyperbola is: \[ \frac{x^2}{a^2} - \frac{y^2}{b^2} = 1 \] or its rotated counterpart. Key characteristics of a hyperbola include:
This is determined when the discriminant (\text{D}) of the conic section is greater than 0 (\text{D} > 0). The standard equation of a hyperbola is: \[ \frac{x^2}{a^2} - \frac{y^2}{b^2} = 1 \] or its rotated counterpart. Key characteristics of a hyperbola include:
- Transverse Axis: This is the line segment that passes through the foci of the hyperbola.
- Conjugate Axis: Perpendicular to the transverse axis, it does not intersect the hyperbola.
- Foci: These are two fixed points that are used in the definition of the hyperbola. The difference between the distances from any point on a hyperbola to the foci is a constant.
- Vertices: Found on the transverse axis, these are the points where each branch of the hyperbola intersects the axis.
Parabola
A parabola is a unique type of conic section characterized by its open, U-shaped curve. This occurs when the discriminant (\text{D}) of the equation equals zero (\text{D} = 0). The standard equation of a parabola, when aligned with its vertex at the origin, is given by: \[ y = ax^2 \] Here, \text{a} determines the width and direction of the parabola. Key features include:
- Vertex: The most significant point, representing the lowest or highest point on the parabola, depending on its orientation.
- Focus: A fixed point inside the parabola. Every point on a parabola is equidistant from the focus and the directrix.
- Directrix: A line outside the parabola. Used with the focus, it helps define the curve.
- Axis of Symmetry: A vertical line through the vertex that divides the parabola into two mirrored halves.