Understanding the Rational Zero Theorem

Oct 13, 2025 by wbrum.org 6 views

Introduction

The rational zero theorem is a fundamental concept in algebra that helps us find the rational zeros of a polynomial function. It states that if a rational number p/q is a zero of the polynomial function f(x), then p must be a factor of the constant term, and q must be a factor of the leading coefficient. In this article, we will use the rational zero theorem to find a rational zero of the polynomial function f(x) = x^3 + 3x^2 - 14x - 20.

Understanding the Rational Zero Theorem

The rational zero theorem is based on the concept of factors and multiples. If a rational number p/q is a zero of the polynomial function f(x), then p must be a factor of the constant term, and q must be a factor of the leading coefficient. This means that if we can find all the factors of the constant term and the leading coefficient, we can list all the possible rational zeros of the polynomial function.

Finding Factors of the Constant Term and Leading Coefficient

To find the factors of the constant term and the leading coefficient, we need to factorize them. The constant term is -20, and the leading coefficient is 1. The factors of -20 are ±1, ±2, ±4, ±5, ±10, and ±20. Since the leading coefficient is 1, its only factor is ±1.

Listing Possible Rational Zeros

Now that we have found the factors of the constant term and the leading coefficient, we can list all the possible rational zeros of the polynomial function. The possible rational zeros are all the combinations of the factors of the constant term and the leading coefficient. In this case, the possible rational zeros are ±1, ±2, ±4, ±5, ±10, and ±20.

Testing Possible Rational Zeros

To find the actual rational zero of the polynomial function, we need to test each of the possible rational zeros. We can do this by substituting each possible rational zero into the polynomial function and checking if it equals zero. If it does, then that rational number is a zero of the polynomial function.

Testing Rational Zero A: 2

Let's start by testing rational zero A: 2. We substitute x = 2 into the polynomial function f(x) = x^3 + 3x^2 - 14x - 20.

f(2) = (2)^3 + 3(2)^2 - 14(2) - 20 f(2) = 8 + 12 - 28 - 20 f(2) = -28

Since f(2) ≠ 0, rational zero A: 2 is not a zero of the polynomial function.

Testing Rational Zero B: -2

Next, let's test rational zero B: -2. We substitute x = -2 into the polynomial function f(x) = x^3 + 3x^2 - 14x - 20.

f(-2) = (-2)^3 + 3(-2)^2 - 14(-2) - 20 f(-2) = -8 + 12 + 28 - 20 f(-2) = 12

Since f(-2) ≠ 0, rational zero B: -2 is not a zero of the polynomial function.

Testing Rational Zero C: 5

Now, let's test rational zero C: 5. We substitute x = 5 into the polynomial function f(x) = x^3 + 3x^2 - 14x - 20.

f(5) = (5)^3 + 3(5)^2 - 14(5) - 20 f(5) = 125 + 75 - 70 - 20 f(5) = 130

Since f(5) ≠ 0, rational zero C: 5 is not a zero of the polynomial function.

Testing Rational Zero D: -5

Next, let's test rational zero D: -5. We substitute x = -5 into the polynomial function f(x) = x^3 + 3x^2 - 14x - 20.

f(-5) = (-5)^3 + 3(-5)^2 - 14(-5) - 20 f(-5) = -125 + 75 + 70 - 20 f(-5) = 0

Since f(-5) = 0, rational zero D: -5 is a zero of the polynomial function.

Conclusion

In this article, we used the rational zero theorem to find a rational zero of the polynomial function f(x) = x^3 + 3x^2 - 14x - 20. We listed all the possible rational zeros of the polynomial function and tested each of them to find the actual rational zero. We found that rational zero D: -5 is a zero of the polynomial function.

Final Answer

The final answer is: D. -5

Introduction

The rational zero theorem is a fundamental concept in algebra that helps us find the rational zeros of a polynomial function. In our previous article, we used the rational zero theorem to find a rational zero of the polynomial function f(x) = x^3 + 3x^2 - 14x - 20. In this article, we will answer some frequently asked questions about the rational zero theorem.

Q: What is the rational zero theorem?

A: The rational zero theorem is a theorem that states that if a rational number p/q is a zero of the polynomial function f(x), then p must be a factor of the constant term, and q must be a factor of the leading coefficient.

Q: How do I find the factors of the constant term and leading coefficient?

A: To find the factors of the constant term and leading coefficient, you need to factorize them. The constant term is -20, and the leading coefficient is 1. The factors of -20 are ±1, ±2, ±4, ±5, ±10, and ±20. Since the leading coefficient is 1, its only factor is ±1.

Q: How do I list all the possible rational zeros?

A: To list all the possible rational zeros, you need to combine all the factors of the constant term and the leading coefficient. In this case, the possible rational zeros are ±1, ±2, ±4, ±5, ±10, and ±20.

Q: How do I test each possible rational zero?

A: To test each possible rational zero, you need to substitute each possible rational zero into the polynomial function and check if it equals zero. If it does, then that rational number is a zero of the polynomial function.

Q: What if I get a non-zero result when testing a possible rational zero?

A: If you get a non-zero result when testing a possible rational zero, then that rational number is not a zero of the polynomial function.

Q: What if I get a zero result when testing a possible rational zero?

A: If you get a zero result when testing a possible rational zero, then that rational number is a zero of the polynomial function.

Q: Can I use the rational zero theorem to find all the zeros of a polynomial function?

A: Yes, you can use the rational zero theorem to find all the zeros of a polynomial function. However, you may need to use other methods, such as synthetic division or the quadratic formula, to find the remaining zeros.

Q: What are some common mistakes to avoid when using the rational zero theorem?

A: Some common mistakes to avoid when using the rational zero theorem include:

Not factoring the constant term and leading coefficient correctly
Not listing all the possible rational zeros
Not testing each possible rational zero correctly
Not checking if the result is zero or non-zero

Conclusion

In this article, we answered some frequently asked questions about the rational zero theorem. We hope that this article has helped you understand the rational zero theorem better and how to use it to find the rational zeros of a polynomial function.

Final Tips

Make sure to factor the constant term and leading coefficient correctly
List all the possible rational zeros
Test each possible rational zero correctly
Check if the result is zero or non-zero

By following these tips, you can use the rational zero theorem to find the rational zeros of a polynomial function with ease.