Chapter 10: Problem 7
Name the conic or limiting form represented by the given equation. Usually you will need to use the process of completing the square (see Examples 3-5). $$ y^{2}-5 x-4 y-6=0 $$
Short Answer
Expert verified
The conic section is a parabola.
Step by step solution
01
Rearrange the Equation
Start with the given equation: \( y^2 - 5x - 4y - 6 = 0 \). Reorganize it to make it easier to complete the square. This involves having all the terms related to \( y \) on one side. Rearrange the equation as \( y^2 - 4y = 5x + 6 \).
02
Complete the Square
Take the \( y \)-related terms from the rearranged equation, \( y^2 - 4y \). To complete the square, take half of the coefficient of \( y \) (which is -4), square it (\((-4/2)^2 = 4\)), and add that inside the equation. Thus, add and subtract 4 on the left side: \( y^2 - 4y + 4 - 4 = 5x + 6 \). This becomes \( (y - 2)^2 - 4 = 5x + 6 \).
03
Simplify the Equation
Move the -4 to the right-hand side to simplify: \( (y - 2)^2 = 5x + 10 \).
04
Identify the Conic Section
Recognize the standard form of the equation. The equation \( (y - 2)^2 = 5(x + 2) \) is in the form \( (y-k)^2 = 4p(x-h) \), which represents a parabola. Thus, the conic section represented by the equation is a parabola.
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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 type of conic section you'll often encounter in mathematics. It looks like a U-shape or an inverted U. The most important things to know about parabolas are:
- They have a vertex, which represents the turning point or the "tip" of the U-shape.
- Parabolas are symmetrical. This means one side is a mirror image of the other.
- Their equation form is either \( y^2 = 4px \) or \( x^2 = 4py \), depending on their orientation – whether they open up, down, left, or right.
Completing the Square
Completing the square is a useful mathematical technique used to simplify quadratic equations. It helps to transform quadratic equations into a form that makes them easy to solve or to identify conic sections.Here’s how to do it:
- Start with a quadratic expression, like \( y^2 - 4y \).
- Find the coefficient of the linear term, here it’s -4, take half of it, square it, and then add and subtract that square from the equation. For example, half of -4 is -2, and \( (-2)^2 = 4 \).
- Re-write the quadratic part of the expression with your new term, so \( y^2 - 4y + 4 \) and subtract 4 to keep the equation balanced. Now it becomes \( (y - 2)^2 - 4 \).
Equations of Conics
Conic sections include shapes like circles, ellipses, parabolas, and hyperbolas. Each has its own special set of equations.Here's a quick guide:
- Circles: Their equation is \( (x-h)^2 + (y-k)^2 = r^2 \).
- Ellipses: Their form resembles circles but stretched, \( \frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1 \).
- Parabolas: Discussed earlier, they follow \( (y-k)^2 = 4p(x-h) \) or \( (x-h)^2 = 4p(y-k) \).
- Hyperbolas: Look like two mirrored curves, with an equation such as \( \frac{(x-h)^2}{a^2} - \frac{(y-k)^2}{b^2} = 1 \).