Chapter 2: Problem 11
Express \(f(x)\) in the form \(a(x-h)^{2}+k\) $$f(x)=-\frac{3}{4} x^{2}+9 x-34$$
Short Answer
Expert verified
The vertex form of \(f(x)\) is \(-\frac{3}{4}(x - 2)^2 - 31\).
Step by step solution
01
Identify the Quadratic Function Terms
The given quadratic function is \(f(x) = -\frac{3}{4} x^{2} + 9x - 34\). This can be related to the standard quadratic form \(ax^2 + bx + c\), where \(a = -\frac{3}{4}\), \(b = 9\), and \(c = -34\).
02
Complete the Square
To express \(f(x)\) in vertex form \(a(x-h)^2 + k\), we need to complete the square. First, factor \(-\frac{3}{4}\) out of the first two terms.\[-\frac{3}{4}(x^2 - \frac{12}{3}x) - 34\]Next, complete the square by finding the term needed to complete the perfect square trinomial. Take half of \(-\frac{12}{3}\), square it, and add and subtract it inside the parentheses:\[-\frac{3}{4}\left((x - \frac{12}{3\cdot2})^2 - (\frac{12}{3\cdot2})^2\right) - 34\]\[-\frac{3}{4}\left((x - 2)^2 - 4\right) - 34\]
03
Simplify the Expression
Distribute \(-\frac{3}{4}\) across the terms inside the parentheses and then adjust the constant term:\[-\frac{3}{4}(x - 2)^2 + \frac{3}{4} \times 4 - 34\]\[-\frac{3}{4}(x - 2)^2 + 3 - 34\]This simplifies to:\[-\frac{3}{4}(x - 2)^2 - 31\]
04
Write the Final Vertex Form
Thus, the expression \(f(x)\) in vertex form is:\(f(x) = -\frac{3}{4}(x - 2)^2 - 31\).Where \(a = -\frac{3}{4}\), \(h = 2\), and \(k = -31\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Quadratic Function
A quadratic function is a type of polynomial equation that can be expressed in the standard form, \(ax^2 + bx + c\), where \(a\), \(b\), and \(c\) are constants and \(a eq 0\). This equation represents a parabola on the coordinate plane. Here are a few key characteristics of a quadratic function:
- It has a degree of 2, which means the highest power of \(x\) is 2.
- The graph of a quadratic function is a curve called a parabola.
- The parabola can open upwards or downwards depending on the sign of \(a\). If \(a > 0\), it opens upwards, and if \(a < 0\), it opens downwards.
- The vertex of the parabola is a significant point that represents the maximum or minimum value of the function.
Completing the Square
Completing the square is a useful algebraic method for rewriting a quadratic function to reveal important features like its vertex. This technique transforms a quadratic from standard form \(ax^2 + bx + c\) into vertex form \(a(x-h)^2+k\). Let’s break down the steps involved:
- First, if \(a\) is not 1, factor \(a\) out from the first two terms. In our example, this means \(-\frac{3}{4}\) is factored out.
- Next, take the coefficient of \(x\) (after factoring, if necessary), divide it by 2, and square it. This value is crucial for forming a perfect square trinomial.
- Add and subtract this squared value inside the parentheses to complete the square. Remember, you should balance the equation by distributing and adjusting terms outside the trinomial as needed.
- The expression inside the parentheses can now be written as \((x-h)^2\), where \(h\) is the value you added and subtracted.
Standard Quadratic Form
The standard quadratic form is the common way of presenting quadratic functions: \(ax^2 + bx + c\). Each part of the formula plays a distinct role:
- \(a\): Determines the direction and "width" of the parabola. A larger absolute value of \(a\) makes the parabola narrower, while a smaller absolute value makes it wider.
- \(b\): Affects the location of the axis of symmetry and, paired with \(a\), impacts the vertex's horizontal position.
- \(c\): Represents the y-intercept, the point where the graph intersects the y-axis.