Chapter 3: Problem 11
Write each quadratic function in the form \(y=a(x-h)^{2}+k\) and sketch its graph. $$y=x^{2}-3 x$$
Short Answer
Expert verified
The vertex form is \[y = (x - \frac{3}{2})^2 - \frac{9}{4}\].
Step by step solution
01
Identify the quadratic function form
The given quadratic function is in the form of \[y = x^2 - 3x\]The goal is to write it in the vertex form \[y = a(x-h)^2 + k\]
02
Complete the square
To rewrite the function in vertex form, complete the square. Start with \[y = x^2 - 3x\]1. Take half of the coefficient of the linear term \((x\text{-coefficient}) = -3\), which is \[-\frac{3}{2}\]2. Square it: \[-\frac{3}{2}^2 = \frac{9}{4}\]3. Add and subtract this square inside the equation:\[y = x^2 - 3x + \frac{9}{4} - \frac{9}{4}\]
03
Re-write as a perfect square trinomial
Group the perfect square trinomial and the constant separately:\[y = (x^2 - 3x + \frac{9}{4}) - \frac{9}{4}\]Rewrite the trinomial as a square:\[y = (x - \frac{3}{2})^2 - \frac{9}{4}\]
04
Identify the parameters
Compare the equation \[y = (x - \frac{3}{2})^2 - \frac{9}{4}\] with the vertex form \[y = a(x - h)^2 + k\]. Here, \[a = 1\], \[h = \frac{3}{2}\], \[k = -\frac{9}{4}\].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Completing the Square
Completing the square is a method used to transform a quadratic equation into its vertex form. This method is particularly useful because it makes it easier to understand and graph the quadratic function.
To complete the square, follow these steps:
To complete the square, follow these steps:
- Start with the quadratic function in standard form: \[y = ax^2 + bx + c\]
- Focus on the quadratic and linear terms: \[ax^2 + bx\]
- Divide all terms by 'a' if 'a' is not equal to 1. For simplicity’s sake, many basic exercises assume 'a' is 1.
- Take half of the coefficient of the linear term (the x-coefficient) and then square it. This value will be added and subtracted inside the equation to create a perfect square trinomial.
- Rewrite the trinomial as a squared binomial.
- Take half of -3: \[ -\frac{3}{2}\]
- Square it: \[ \left(- \frac{3}{2} \right)^2 = \frac{9}{4}\]
- Add and subtract this value: \[ y = x^2 - 3x + \frac{9}{4} - \frac{9}{4} \]
- Group the perfect square trinomial and the constant separately: \[ y = \left( x - \frac{3}{2} \right)^2 - \frac{9}{4} \]
Quadratic Functions
A quadratic function is a second-degree polynomial function of the form \[ y = ax^2 + bx + c \]. The graph of a quadratic function is a parabola that opens upwards if the coefficient 'a' is positive and downwards if 'a' is negative.
The vertex form of a quadratic function is \[ y = a(x-h)^2 + k \], where (h, k) represents the vertex of the parabola.
Understanding the vertex form is beneficial because:
The vertex form of a quadratic function is \[ y = a(x-h)^2 + k \], where (h, k) represents the vertex of the parabola.
Understanding the vertex form is beneficial because:
- It clearly shows the vertex point, making it easier to graph the function.
- It highlights how the parabola is shifted relative to the origin.
Rewriting Equations
Rewriting a quadratic function into its vertex form involves completing the square. This process not only helps in expressing the function in a more insightful form but also simplifies the graphing process.
Here's a concise breakdown of the rewriting process applied to the original equation \[ y = x^2 - 3x\]:
Here's a concise breakdown of the rewriting process applied to the original equation \[ y = x^2 - 3x\]:
- Identify the terms to complete the square: \[ x^2 - 3x \]
- Take half of the x-coefficient and square it: \[ \left( -\frac{3}{2} \right)^2 = \frac{9}{4} \]
- Add and subtract this value: \[ y = x^2 - 3x + \frac{9}{4} - \frac{9}{4} \]
- Rewrite as a perfect square trinomial: \[ y = \left( x - \frac{3}{2} \right)^2 - \frac{9}{4} \]