Chapter 10: Problem 42
Without writing the equation in standard form, state whether the graph of each equation is a parabola, circle, ellipse, or hyperbola. $$ 2 x^{2}+12 x+18-y^{2}=3\left(2-y^{2}\right)+4 y $$
Short Answer
Expert verified
The graph is a hyperbola.
Step by step solution
01
Simplify both sides separately
Start by simplifying both sides of the given equation \( 2x^2 + 12x + 18 - y^2 = 3(2 - y^2) + 4y \). The left side is already expanded. For the right side, distribute the 3 in the term \( 3(2-y^2) \). This results in \( 6 - 3y^2 + 4y \).
02
Rearrange terms to detect the conic section
Now, write both sides in one equation: \( 2x^2 + 12x + 18 - y^2 = 6 - 3y^2 + 4y \). Move all terms to one side to begin analyzing the conic type: \( 2x^2 + 12x + y^2 - 3y^2 - 4y + 18 - 6 = 0 \). Simplifying the equation, you get: \( 2x^2 + 12x - 2y^2 - 4y + 12 = 0 \).
03
Identify the conic based on coefficients
Identify the type of conic section based on the coefficients. Notice the squared terms: there is a \( x^2 \) term and a \( y^2 \) term with opposite signs (\( 2x^2 - 2y^2 \)). This indicates the presence of both positive and negative terms indicates the conic is a hyperbola.
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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 unique and simple conic section that you can recognize by its U-shaped curve. The standard form of a parabolic equation is either \( y = ax^2 + bx + c \) or \( x = ay^2 + by + c \). A parabola has a single axis of symmetry and a single point known as the vertex, which represents the highest or lowest point on the graph depending on its orientation. There are several key characteristics:
- Vertex: The turning point of the parabola.
- Focus: A point inside the parabola that helps define its shape.
- Directrix: A line outside the parabola that is equidistant from the vertex as the focus is.
- Axis of Symmetry: A line that divides the parabola into two mirror images.
Circle
Circles are perhaps the most well-known conic sections. They are defined as the set of all points in a plane that are equidistant from a given point called the center. The equation for a circle can be written in standard form as \( (x - h)^2 + (y - k)^2 = r^2 \), where \((h, k)\) represents the center, and \(r\) is the radius. Circles have several key properties:
- Center: The middle point from which all points on the circle are equidistant.
- Radius: The distance from any point on the circle to its center.
- Diameter: A straight line that passes through the center of the circle, connecting two points on its edge, and is twice the radius.
- Circumference: The perimeter or boundary length of the circle.
Ellipse
An ellipse is an oblong shape that resembles a stretched or squashed circle. It is represented by the standard equation \( \frac{(x - h)^2}{a^2} + \frac{(y - k)^2}{b^2} = 1 \), where \( (h, k) \) is the center, \( a \) is the semi-major axis, and \( b \) is the semi-minor axis. Key features of ellipses include:
- Foci: Two points inside the ellipse that help to define the shape.
- Major Axis: The longest diameter of the ellipse that passes through its center.
- Minor Axis: The shortest diameter perpendicular to the major axis.
- Eccentricity: A measure of how elongated the ellipse is.
Hyperbola
A hyperbola consists of two symmetrical open curves. It is represented by the equation \( \frac{(x - h)^2}{a^2} - \frac{(y - k)^2}{b^2} = 1 \) or its alternate form when \( y^2 \) precedes the \( x^2 \). Hyperbolas have two branches that mirror each other, and their key characteristics include:
- Foci: Two points from which distances are measured in defining the curve.
- Vertices: The points where each branch of the hyperbola is closest to its center.
- Asymptotes: Lines that the branches approach but never touch. They provide a framework for the curve.
- Center: The midpoint between the vertices (and foci).