Chapter 4: Problem 106
a. Find the coordinates of the vertex of the parabola$$y=a x^{2}+b x+c, a \neq 0$$. b. When is the parabola concave up? Concave down? Give reasons for your answers.
Short Answer
Expert verified
The vertex is \((-\frac{b}{2a}, y_\text{vertex})\). The parabola is concave up if \(a > 0\) and concave down if \(a < 0\).
Step by step solution
01
Identify the standard form of the parabola
The given equation is in the form \( y = ax^2 + bx + c \), which is a quadratic equation representing a parabola.
02
Use the vertex formula
To find the vertex of the parabola, use the vertex formula. The x-coordinate of the vertex is given by \( x = -\frac{b}{2a} \). Substitute this value back into the equation \( y = ax^2 + bx + c \) to find the y-coordinate of the vertex.
03
Calculate the x-coordinate
Compute \( x_\text{vertex} = -\frac{b}{2a} \). This is the x-coordinate of the vertex of the parabola.
04
Calculate the y-coordinate
Substitute \( x_\text{vertex} \) into the equation \( y = ax^2 + bx + c \) to find \( y_\text{vertex} \). The vertex is \( (x_\text{vertex}, y_\text{vertex}) \).
05
Determine concavity condition (Concave Up)
If \( a > 0 \), the parabola opens upwards, and thus it is concave up.
06
Determine concavity condition (Concave Down)
If \( a < 0 \), the parabola opens downwards, and thus it is concave down.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vertex of a Parabola
To locate the vertex of a parabola, it's crucial to understand that it is the point where the parabola changes direction. For a parabola defined by the quadratic equation \( y = ax^2 + bx + c \), the vertex formula allows us to easily find its coordinates. The x-coordinate of the vertex can be found using: \[ x_{\text{vertex}} = -\frac{b}{2a} \]Once you have the x-coordinate, plug this value back into the original quadratic equation to find the y-coordinate, giving you the vertex coordinates \((x_{\text{vertex}}, y_{\text{vertex}})\). **Steps to Find the Vertex**:
- Identify coefficients \(a\), \(b\), and \(c\) from the equation.
- Compute \(x_{\text{vertex}} = -\frac{b}{2a}\).
- Substitute \(x_{\text{vertex}}\) back into the equation to determine \(y_{\text{vertex}}\).
Concavity
Concavity describes how a parabola curves. Whether a parabola is concave up or concave down is primarily determined by the coefficient \(a\) in the quadratic equation \(y = ax^2 + bx + c\). Concavity is a key concept in understanding the shape of a parabola.**Concave Up**:
- If \(a > 0\), the parabola opens upwards.
- This configuration resembles a smiling mouth, forming a "U" shape.
- In this case, the vertex represents the lowest point, or the minimum of the parabola.
- If \(a < 0\), the parabola opens downwards.
- This makes the parabola look like a frowning mouth, resembling an upside-down "U" shape.
- Here, the vertex represents the highest point, or the maximum of the parabola.
Quadratic Equations
Quadratic equations are polynomial equations of degree two, generally represented in standard form as \( y = ax^2 + bx + c \), where \(a\), \(b\), and \(c\) are constants, and \(a eq 0\). These equations form the basis for parabolas in coordinate geometry and appear frequently in mathematical analysis.**Features of Quadratic Equations**:
- They have a set of solutions called roots, which can be real or complex.
- The graph of a quadratic equation is a parabola, providing visual insights into the equation's behavior.
- The sign of \(a\) determines the concavity of the parabola.
- They can be solved using various methods including factoring, completing the square, or using the quadratic formula \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\).