Chapter 2: Problem 16
(a) Use the quadratic formula to find the zeros of \(f .\) (b) Find the maximum or minimum value of \(f(x)\) (c) Sketch the graph of \(f\) $$f(x)=6 x^{2}+7 x-24$$
Short Answer
Expert verified
Zeros are \(\frac{3}{2}\) and \(-\frac{8}{3}\); Minimum is at \((-\frac{7}{12}, -25.04)\). The graph is a parabola opening upwards.
Step by step solution
01
Identify the coefficients
The quadratic function given is \(f(x) = 6x^2 + 7x - 24\). Identify the coefficients \(a\), \(b\), and \(c\) where \(a = 6\), \(b = 7\), and \(c = -24\).
02
Apply the quadratic formula
The quadratic formula is \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \). Substitute the values of \(a\), \(b\), and \(c\) into the formula: \( x = \frac{-7 \pm \sqrt{7^2 - 4 \times 6 \times (-24)}}{2 \times 6} \).
03
Calculate the discriminant
Calculate \(b^2 - 4ac\): \(7^2 - 4(6)(-24) = 49 + 576 = 625\). Since the discriminant is positive, there are two real solutions.
04
Solve for the zeros
Use the discriminant to find the zeros: \( x = \frac{-7 \pm \sqrt{625}}{12} \). Simplify the square root: \(\sqrt{625} = 25\). So, \( x = \frac{-7 \pm 25}{12}\).This gives two solutions: \( x_1 = \frac{18}{12} = \frac{3}{2}\) and \( x_2 = \frac{-32}{12} = -\frac{8}{3}\).
05
Determine the vertex
The vertex form is given by the formula \(x = -\frac{b}{2a}\). Substitute \(b = 7\) and \(a = 6\): \(x = -\frac{7}{12}\).
06
Calculate the minimum value
Substitute \(x = -\frac{7}{12}\) back into the function to find \(f(x)\): \(f\left(-\frac{7}{12}\right) = 6\left(-\frac{7}{12}\right)^2 + 7\left(-\frac{7}{12}\right) - 24\). Simplify to find the minimum value \(f(x)\).
07
Completing the square for \(y\)-intercept
Identify the \(y\)-intercept by substituting \(x = 0\) into \(f(x)\): \(f(0) = -24\).
08
Description of the graph
The parabola opens upwards because \(a > 0\), has \(x\)-intercepts at \(\frac{3}{2}\) and \(-\frac{8}{3}\), and a minimum point. The \(y\)-intercept is \(-24\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Quadratic Formula
The Quadratic Formula is a vital tool when working with quadratic functions, especially to find the zeros or solutions of the equation. A quadratic equation is typically in the form \(ax^2 + bx + c = 0\), where \(a\), \(b\), and \(c\) are coefficients. To find the solutions, or roots, we use the formula:
\[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\]
This formula derives from the process of completing the square and is applicable when the quadratic equation cannot be factored easily. It gives us a way to find complex and real solutions.
Key points about using the Quadratic Formula:
\[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\]
This formula derives from the process of completing the square and is applicable when the quadratic equation cannot be factored easily. It gives us a way to find complex and real solutions.
Key points about using the Quadratic Formula:
- Always identify \(a\), \(b\), and \(c\) from your quadratic equation first.
- \(-b\) is the opposite of the \(b\) coefficient.
- Use discriminant \(b^2 - 4ac\) to assess the number and type of solutions.
- The solutions \(x_1\) and \(x_2\) include "\(\pm\)" indicating two potential values.
Discriminant
The discriminant is an essential part of the quadratic formula that provides insight into the nature of the roots of a quadratic equation. It is the expression under the square root in the quadratic formula, denoted as \(b^2 - 4ac\). The discriminant helps us understand whether the solutions are real or complex, and distinct or repeated.
Consider the following scenarios:
Consider the following scenarios:
- If \(b^2 - 4ac > 0\), the quadratic equation has two distinct real roots. This means the graph will intersect the x-axis in two points.
- If \(b^2 - 4ac = 0\), there is exactly one real root (also called a repeated or double root), meaning the vertex of the parabola touches the x-axis.
- If \(b^2 - 4ac < 0\), the roots are complex, and the graph does not intersect the x-axis.
Vertex of a Parabola
The vertex of a parabola is a significant feature in the context of a quadratic function. It is either the highest or lowest point on the graph, depending on whether the parabola opens upwards or downwards. The x-coordinate of the vertex can be efficiently computed using the formula \(x = -\frac{b}{2a}\). This formula is derived from completing the square method and represents the axis of symmetry of the parabola.
Once the x-coordinate of the vertex is known, substitute it back into the quadratic function to find the corresponding y-coordinate, which gives the full vertex point \((x, f(x))\).
In our equation, \(f(x) = 6x^2 + 7x - 24\), with \(a = 6\) and \(b = 7\), the vertex's x-coordinate is \(-\frac{7}{12}\). By substituting this back into the function, we can ascertain the minimum value of the quadratic, as this parabola opens upwards (since \(a > 0\)). The vertex is quite useful:
Once the x-coordinate of the vertex is known, substitute it back into the quadratic function to find the corresponding y-coordinate, which gives the full vertex point \((x, f(x))\).
In our equation, \(f(x) = 6x^2 + 7x - 24\), with \(a = 6\) and \(b = 7\), the vertex's x-coordinate is \(-\frac{7}{12}\). By substituting this back into the function, we can ascertain the minimum value of the quadratic, as this parabola opens upwards (since \(a > 0\)). The vertex is quite useful:
- It determines the direction of the parabola: upward (minimum) or downward (maximum).
- It provides key graphing insights, serving as a reference point for drawing the parabola.
Zeros of a Function
The zeros of a function, also known as its roots or solutions, are the values of \(x\) for which the function \(f(x) = 0\). These are the points where the graph of the function intersects the x-axis.
Finding the zeros is crucial as it provides fundamental insights into the behavior of the quadratic function.
In a quadratic equation like \(f(x) = 6x^2 + 7x - 24\), using the Quadratic Formula reveals the zeros: \(x_1 = \frac{3}{2}\) and \(x_2 = -\frac{8}{3}\).
These zeros show where the parabola crosses the x-axis.The importance of zeros can be summarized as:
Finding the zeros is crucial as it provides fundamental insights into the behavior of the quadratic function.
In a quadratic equation like \(f(x) = 6x^2 + 7x - 24\), using the Quadratic Formula reveals the zeros: \(x_1 = \frac{3}{2}\) and \(x_2 = -\frac{8}{3}\).
These zeros show where the parabola crosses the x-axis.The importance of zeros can be summarized as:
- They define the x-intercepts of the function.
- They are solutions to the equation \(f(x) = 0\).
- Knowing them helps in sketching the graph, providing a clear visual representation of the function's behavior.