Chapter 13: Problem 79
Write each equation in standard form, if it is not alreacty so, and graph it. If the graph is a circle, give the coordinates of its center and its radius. If the graph is a parabola, give the coordinates of its vertex. $$ x=\frac{1}{2} y^{2}+2 y $$
Short Answer
Expert verified
The equation is a parabola with vertex at \((-2, -2)\).
Step by step solution
01
Understand the Equation
The given equation is a quadratic in terms of y: \( x = \frac{1}{2}y^2 + 2y \). This form suggests that it is a parabola, opening along the x-axis (since it is quadratic in y).
02
Rearrange the Equation
To express the equation in the standard form of a parabola, rearrange it. The standard form for a parabola opening to the right is \( (y - k)^2 = 4p(x - h) \). Rewrite by completing the square:\( x = \frac{1}{2}y^2 + 2y \) can be rewritten as \( x = \frac{1}{2}(y^2 + 4y) \).Complete the square for \( y^2 + 4y \). First, find \( (\frac{4}{2})^2 = 4 \). Add and subtract 4 inside the parentheses:\( x = \frac{1}{2}((y^2 + 4y + 4) - 4) \).Simplifies to \( x = \frac{1}{2}((y + 2)^2 - 4) \).Distribute the \( \frac{1}{2} \):\( x = \frac{1}{2}(y + 2)^2 - 2 \).This is equivalent to \( (y + 2)^2 = 2(x + 2) \), which is now in standard form.
03
Identify the Vertex
The standard form of the parabola is \( (y + 2)^2 = 2(x + 2) \). Identify the vertex \( (h, k) \) from this form: \( h = -2 \) and \( k = -2 \). Thus, the vertex is at \( (-2, -2) \).
04
Graph the Parabola
Plot the vertex at \((-2, -2)\). Since the equation is of the form \((y - k)^2 = 4p(x - h)\), the parabola opens to the right. The distance \(p\), calculated from \(4p = 2\), gives \(p = \frac{1}{2}\). Mark points to the right side of the vertex, 0.5 units away, to show the direction and opening width.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Standard Form
The term "standard form" in relation to a parabola is an important concept. It provides a way to express parabolic equations in a manner that makes them easy to analyze and graph. For a parabola that opens horizontally (such as with the variable relationship given by the exercise), the standard form is: \((y - k)^2 = 4p(x - h)\).
In this equation:
In this equation:
- \(h\) and \(k\) are the coordinates of the vertex of the parabola.
- \(p\) is the distance from the vertex to the focus, which also determines whether the parabola opens to the right or left.
Completing the Square
Completing the square is a technique used to convert a quadratic equation into a form that reveals significant properties, like the vertex of a parabola. It is especially handy when we need to rewrite quadratic equations that are not immediately in a standard form.
To start completing the square for the equation \(x = \frac{1}{2} y^2 + 2y\), we focus on the quadratic expression in \(y\): \(y^2 + 4y\). Here's the step-by-step method:
To start completing the square for the equation \(x = \frac{1}{2} y^2 + 2y\), we focus on the quadratic expression in \(y\): \(y^2 + 4y\). Here's the step-by-step method:
- First, find the constant that makes \(y^2 + 4y\) a perfect square trinomial. Take half of the linear coefficient \(4\) and square it: \(\left(\frac{4}{2}\right)^2 = 4\).
- Now, add and subtract this constant inside the expression to form a perfect square trinomial: \((y^2 + 4y + 4 - 4)\).
- Rewrite \((y^2 + 4y + 4)\) as \((y + 2)^2\) simplifying the form.
- This manipulation transforms the equation to \(x = \frac{1}{2}((y + 2)^2 - 4)\), which simplifies further to \((y + 2)^2 = 2(x + 2)\).
Graphing Parabolas
Graphing a parabola becomes straightforward once the equation is in its standard form. For the given problem, our equation is \((y + 2)^2 = 2(x + 2)\), which is in the standard form \((y - k)^2 = 4p(x - h)\).
Let's break down the graphing process:
Let's break down the graphing process:
- Start by plotting the vertex, which is at the point \((-2, -2)\). This serves as a pivotal feature of the graph.
- The parameter \(p\) determines how the parabola opens. Since \(4p = 2\), we find \(p = \frac{1}{2}\), indicating a sideways opening (rightward in this case).
- From the vertex, move \(p\) units to the right to locate the focus, assisting in defining the parabola's orientation and width.
- The initial width and direction can be showcased by marking additional points at regular \(p\) intervals along the parabolic path, establishing the symmetrical curve.