How to Write a Quadratic Function with Given Zeros

Oct 13, 2025 by wbrum.org 110 views

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Introduction

In algebra, a quadratic function is a polynomial function of degree two, which means the highest power of the variable is two. The general form of a quadratic function is $f(x) = ax^2 + bx + c$ , where $a$ , $b$ , and $c$ are constants. In this article, we will focus on writing a quadratic function whose zeros are given.

What are Zeros of a Quadratic Function?

The zeros of a quadratic function are the values of $x$ for which the function becomes zero. In other words, if we substitute the zero of a quadratic function into the function, the result will be zero. For example, if we have a quadratic function $f(x) = x^2 - 4$ , the zeros of this function are $x = 2$ and $x = -2$ because when we substitute $x = 2$ or $x = -2$ into the function, the result is zero.

How to Write a Quadratic Function with Given Zeros

To write a quadratic function with given zeros, we can use the factored form of a quadratic function, which is $f(x) = a(x - r_1)(x - r_2)$ , where $r_1$ and $r_2$ are the zeros of the function. In our case, the zeros are given as -3 and -4.

Step 1: Write the Factored Form of the Quadratic Function

Using the factored form of a quadratic function, we can write the function as $h(x) = a(x + 3)(x + 4)$ .

Step 2: Expand the Factored Form

To expand the factored form, we can use the distributive property of multiplication. We multiply the first term in each parentheses by each term in the other parentheses.

$h(x) = a(x + 3)(x + 4)$ $h(x) = a(x^2 + 4x + 3x + 12)$ $h(x) = a(x^2 + 7x + 12)$

Step 3: Determine the Value of $a$

Since we want the function to have zeros at $x = -3$ and $x = -4$ , we can choose any value for $a$ except zero. Let's choose $a = 1$ for simplicity.

$h(x) = 1(x^2 + 7x + 12)$ $h(x) = x^2 + 7x + 12$

Conclusion

In this article, we learned how to write a quadratic function whose zeros are given. We used the factored form of a quadratic function and expanded it to get the standard form of the function. We also determined the value of $a$ to be 1 for simplicity. The final quadratic function is $h(x) = x^2 + 7x + 12$ .

Example Problems

Problem 1

Write a quadratic function whose zeros are 2 and 5.

Solution

Using the factored form of a quadratic function, we can write the function as $f(x) = a(x - 2)(x - 5)$ . Expanding the factored form, we get $f(x) = a(x^2 - 7x + 10)$ . Let's choose $a = 1$ for simplicity. The final quadratic function is $f(x) = x^2 - 7x + 10$ .

Problem 2

Write a quadratic function whose zeros are -1 and 3.

Solution

Using the factored form of a quadratic function, we can write the function as $g(x) = a(x + 1)(x - 3)$ . Expanding the factored form, we get $g(x) = a(x^2 - 2x - 3)$ . Let's choose $a = 1$ for simplicity. The final quadratic function is $g(x) = x^2 - 2x - 3$ .

Applications of Quadratic Functions

Quadratic functions have many applications in real-life situations. Some examples include:

Projectile Motion: The trajectory of a projectile, such as a thrown ball or a rocket, can be modeled using a quadratic function.
Optimization: Quadratic functions can be used to optimize functions, such as finding the maximum or minimum value of a function.
Physics: Quadratic functions are used to model the motion of objects under the influence of gravity or other forces.
Engineering: Quadratic functions are used to design and optimize systems, such as bridges or buildings.

Conclusion

In conclusion, quadratic functions are an important concept in algebra and have many applications in real-life situations. We learned how to write a quadratic function whose zeros are given and how to expand the factored form to get the standard form of the function. We also saw some examples of quadratic functions and their applications.

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Introduction

In our previous article, we learned how to write a quadratic function whose zeros are given. In this article, we will answer some frequently asked questions about quadratic functions.

Q: What is the difference between a quadratic function and a linear function?

A: A linear function is a polynomial function of degree one, which means the highest power of the variable is one. A quadratic function, on the other hand, is a polynomial function of degree two, which means the highest power of the variable is two.

Q: How do I determine the zeros of a quadratic function?

A: To determine the zeros of a quadratic function, you can use the factored form of the function, which is $f(x) = a(x - r_1)(x - r_2)$ , where $r_1$ and $r_2$ are the zeros of the function. You can also use the quadratic formula, which is $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$ .

Q: Can a quadratic function have more than two zeros?

A: No, a quadratic function can only have two zeros. This is because the degree of a quadratic function is two, which means the highest power of the variable is two. Therefore, a quadratic function can only have two roots or zeros.

Q: How do I graph a quadratic function?

A: To graph a quadratic function, you can use the factored form of the function, which is $f(x) = a(x - r_1)(x - r_2)$ . You can also use the quadratic formula to find the zeros of the function and then plot the points on a coordinate plane. Finally, you can draw a smooth curve through the points to get the graph of the function.

Q: What is the vertex of a quadratic function?

A: The vertex of a quadratic function is the point on the graph of the function where the function changes from decreasing to increasing or vice versa. The vertex can be found using the formula $x = -\frac{b}{2a}$ .

Q: Can a quadratic function be negative?

A: Yes, a quadratic function can be negative. In fact, a quadratic function can be negative for all values of $x$ , positive for all values of $x$ , or negative for some values of $x$ and positive for other values of $x$ .

Q: How do I find the maximum or minimum value of a quadratic function?

A: To find the maximum or minimum value of a quadratic function, you can use the factored form of the function, which is $f(x) = a(x - r_1)(x - r_2)$ . You can also use the quadratic formula to find the zeros of the function and then plot the points on a coordinate plane. Finally, you can draw a smooth curve through the points to get the graph of the function and find the maximum or minimum value.

Q: What is the domain of a quadratic function?

A: The domain of a quadratic function is all real numbers, which means that the function is defined for all values of $x$ .

Q: Can a quadratic function be a rational function?

A: No, a quadratic function cannot be a rational function. A rational function is a function that can be written in the form $f(x) = \frac{p(x)}{q(x)}$ , where $p(x)$ and $q(x)$ are polynomials. A quadratic function, on the other hand, is a polynomial function of degree two.

Q: How do I simplify a quadratic function?

A: To simplify a quadratic function, you can use the factored form of the function, which is $f(x) = a(x - r_1)(x - r_2)$ . You can also use the quadratic formula to find the zeros of the function and then plot the points on a coordinate plane. Finally, you can draw a smooth curve through the points to get the graph of the function and simplify the function.

Conclusion

In conclusion, quadratic functions are an important concept in algebra and have many applications in real-life situations. We answered some frequently asked questions about quadratic functions and provided examples and explanations to help you understand the concepts better.

Example Problems

Problem 1

Find the zeros of the quadratic function $f(x) = x^2 + 5x + 6$ .

Solution

Using the factored form of the function, we can write the function as $f(x) = (x + 2)(x + 3)$ . Therefore, the zeros of the function are $x = -2$ and $x = -3$ .

Problem 2

Graph the quadratic function $f(x) = x^2 - 4x + 4$ .

Solution

Using the factored form of the function, we can write the function as $f(x) = (x - 2)^2$ . Therefore, the graph of the function is a parabola that opens upward and has a vertex at $x = 2$ .

Problem 3

Find the maximum value of the quadratic function $f(x) = x^2 - 6x + 8$ .

Solution

Using the factored form of the function, we can write the function as $f(x) = (x - 2)(x - 4)$ . Therefore, the maximum value of the function is $f(2) = 0$ .

Applications of Quadratic Functions

Quadratic functions have many applications in real-life situations. Some examples include:

Projectile Motion: The trajectory of a projectile, such as a thrown ball or a rocket, can be modeled using a quadratic function.
Optimization: Quadratic functions can be used to optimize functions, such as finding the maximum or minimum value of a function.
Physics: Quadratic functions are used to model the motion of objects under the influence of gravity or other forces.
Engineering: Quadratic functions are used to design and optimize systems, such as bridges or buildings.