Chapter 3: Problem 60
Find the equation of the quadratic function satisfying the given conditions. (Hint: Determine values of \(a\), \(h,\) and \(k\) that satisfy \(P(x)=a(x-h)^{2}+k .\) ) Express your answer in the form \(P(x)=a x^{2}+b x+c\). Use your calculator to support your results. Vertex \((5,6) ;\) through \((1,-6)\)
Short Answer
Expert verified
The quadratic equation is \(P(x) = -\frac{3}{4}x^2 + \frac{15}{2}x - \frac{51}{4}\).
Step by step solution
01
Understand the Vertex Form
The vertex form of a quadratic function is \( P(x) = a(x-h)^2 + k \), where \( (h, k) \) is the vertex of the parabola. From the provided data, we know the vertex is \((5, 6)\), so \(h = 5\) and \(k = 6\).
02
Substitute Vertex into Vertex Form
Substitute \(h = 5\) and \(k = 6\) into the vertex form. The equation becomes: \[ P(x) = a(x-5)^2 + 6 \]
03
Use the Additional Point to Find \(a\)
The quadratic passes through the point \((1, -6)\). Substitute \(x = 1\) and \(P(x) = -6\) into the equation to solve for \(a\):\[ -6 = a(1-5)^2 + 6 \]\[ -6 = a(16) + 6 \]Solving for \(a\) gives: \[ -12 = 16a \]\[ a = -\frac{12}{16} = -\frac{3}{4} \]
04
Construct the Equation in Vertex Form
Now that \(a = -\frac{3}{4}\), substitute it back into the vertex form: \[ P(x) = -\frac{3}{4}(x-5)^2 + 6 \]
05
Expand to Standard Form
Expand \((x-5)^2\) and substitute back:\[ P(x) = -\frac{3}{4}((x^2 - 10x + 25)) + 6 \] Distribute \(-\frac{3}{4}\): \[ = -\frac{3}{4}x^2 + \frac{30}{4}x - \frac{75}{4} + 6 \] Combine constants: Convert 6 to \(\frac{24}{4}\): \[ -\frac{75}{4} + \frac{24}{4} = -\frac{51}{4} \]Hence, the standard form is: \[ P(x) = -\frac{3}{4}x^2 + \frac{30}{4}x - \frac{51}{4} \]
06
Simplify Coefficients
Simplify the coefficients for clarity:\[ P(x) = -\frac{3}{4}x^2 + \frac{15}{2}x - \frac{51}{4} \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vertex Form
The vertex form of a quadratic function captures the essence of the parabola's shape by focusing on its vertex. The equation is given by \( P(x) = a(x-h)^2 + k \).
Here:
This form is very useful for finding a quadratic equation when given the vertex and another point on the parabola.
Here:
- \(a\) controls the width and direction of the parabola.
- \(h\) and \(k\) denote the vertex's position on the coordinate plane.
This form is very useful for finding a quadratic equation when given the vertex and another point on the parabola.
Standard Form
Switching a quadratic equation to the standard form can offer a more straightforward look at the coefficients that influence its graph. The standard form is: \( P(x) = ax^2 + bx + c \).
Key points of standard form are:
This form is especially beneficial for analyzing the effects of changes in \(a\), \(b\), and \(c\) on the position and shape of the parabola.
Key points of standard form are:
- \(a\) dictates the parabola’s direction; a positive \(a\) opens upwards and a negative \(a\) opens downwards.
- \(b\) affects the tilt of the parabola.
- \(c\) represents the y-intercept, the point where the parabola crosses the y-axis.
- Multiply out the squared term in \((x-h)^2\).
- Distribute the \(a\) value.
- Combine like terms.
This form is especially beneficial for analyzing the effects of changes in \(a\), \(b\), and \(c\) on the position and shape of the parabola.
Parabola
A parabola is a U-shaped curve which can open upwards or downwards, dictated by the sign of the \(a\) coefficient in the quadratic function.
It is symmetric around a vertical line called the axis of symmetry, which passes through the vertex.Understanding parabolas starts with recognizing their essential features:
It is symmetric around a vertical line called the axis of symmetry, which passes through the vertex.Understanding parabolas starts with recognizing their essential features:
- The vertex: The highest or lowest point on the graph, depending on whether the parabola opens downwards or upwards.
- The axis of symmetry: A vertical line that splits the parabola into two mirror-image halves.
Quadratic Equation
A quadratic equation is a fundamental form of a polynomial equation of degree two.
The general structure is noted as \( ax^2 + bx + c = 0 \), where \(a eq 0\).
Key aspects of quadratic equations include:
The general structure is noted as \( ax^2 + bx + c = 0 \), where \(a eq 0\).
Key aspects of quadratic equations include:
- The coefficient \(a\) must be non-zero to preserve the equation's quadratic nature.
- The solutions or roots of the quadratic, given by the values of \(x\) that satisfy the equation.
- Factoring the quadratic if possible.
- Using the Quadratic Formula: \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \).
- Completing the square, which involves manipulating the equation to derive the vertex form.