Dividing the Polynomial by the Factor

Oct 13, 2025 by wbrum.org 14 views

Introduction

When given a polynomial and one of its zeros, we can use this information to find the other zeros of the polynomial. In this case, we are given the cubic polynomial $P(x) = x^3 - 7x^2 + 19x - 13$ and one of its zeros, $3 + 2i$ . Our goal is to find the other two zeros of the polynomial.

Complex Conjugate Zeros

Since we are given a complex zero, $3 + 2i$ , we know that its complex conjugate, $3 - 2i$ , is also a zero of the polynomial. This is because complex zeros always come in conjugate pairs.

Dividing the Polynomial by the Factor

To find the other zero, we can divide the polynomial $P(x)$ by the factor $(x - (3 + 2i))$ . This will give us a quadratic polynomial that has the other zero as one of its roots.

Using the Complex Conjugate Root Theorem

Since we know that the complex conjugate of $3 + 2i$ is also a zero, we can use the complex conjugate root theorem to find the other zero. The complex conjugate root theorem states that if $a + bi$ is a zero of a polynomial with real coefficients, then $a - bi$ is also a zero of the polynomial.

Finding the Quadratic Factor

To find the quadratic factor, we can use the fact that the product of the factors is equal to the original polynomial. In this case, we have:

P(x) = (x - (3 + 2i))(x - (3 - 2i))(x - r)

where $r$ is the other zero of the polynomial.

Expanding the Product

Expanding the product, we get:

P(x) = (x^2 - 6x + 13)(x - r)

Multiplying the Factors

Multiplying the factors, we get:

P(x) = x^3 - rx^2 - 6x^2 + 6rx + 13x - 13r

Combining Like Terms

Combining like terms, we get:

P(x) = x^3 - (r + 6)x^2 + (6r + 13)x - 13r

Equating Coefficients

Equating the coefficients of the original polynomial and the expanded polynomial, we get:

-7 = -(r + 6)

19 = 6r + 13

Solving for r

Solving the first equation for $r$ , we get:

r = -1

Checking the Solution

Substituting $r = -1$ into the second equation, we get:

19 = 6(-1) + 13

19 = -6 + 13

19 = 7

This is not true, so $r = -1$ is not a solution.

Finding the Correct Solution

Let's go back to the equation:

19 = 6r + 13

Subtracting 13 from both sides, we get:

6 = 6r

Dividing both sides by 6, we get:

r = 1

Checking the Solution

Substituting $r = 1$ into the first equation, we get:

-7 = -(1 + 6)

-7 = -7

This is true, so $r = 1$ is a solution.

Conclusion

In conclusion, the other two zeros of the polynomial $P(x) = x^3 - 7x^2 + 19x - 13$ are $3 - 2i$ and $1$ .

Final Answer

The final answer is: $\boxed{3 - 2i, 1}$

Q: What is the complex conjugate root theorem?

A: The complex conjugate root theorem states that if $a + bi$ is a zero of a polynomial with real coefficients, then $a - bi$ is also a zero of the polynomial.

Q: Why do complex zeros always come in conjugate pairs?

A: Complex zeros always come in conjugate pairs because the coefficients of the polynomial are real numbers. This means that the imaginary parts of the zeros must cancel each other out when the polynomial is expanded.

Q: How do I find the other zero of a cubic polynomial when given one of its zeros?

A: To find the other zero of a cubic polynomial when given one of its zeros, you can divide the polynomial by the factor $(x - (3 + 2i))$ . This will give you a quadratic polynomial that has the other zero as one of its roots.

Q: What is the difference between a zero and a root of a polynomial?

A: A zero of a polynomial is a value of $x$ that makes the polynomial equal to zero. A root of a polynomial is also a value of $x$ that makes the polynomial equal to zero.

Q: Can a polynomial have more than one zero?

A: Yes, a polynomial can have more than one zero. In fact, a cubic polynomial can have up to three zeros.

Q: How do I know if a zero is real or complex?

A: You can determine if a zero is real or complex by looking at the coefficients of the polynomial. If the coefficients are real numbers, then the zeros will be either real or complex conjugates.

Q: Can a polynomial have a zero that is not a real number?

A: Yes, a polynomial can have a zero that is not a real number. In fact, complex zeros are a common occurrence in polynomials with real coefficients.

Q: How do I find the complex conjugate of a zero?

A: To find the complex conjugate of a zero, you simply change the sign of the imaginary part. For example, if the zero is $3 + 2i$ , then the complex conjugate is $3 - 2i$ .

Q: Can a polynomial have a zero that is a complex number with a non-zero imaginary part?

A: Yes, a polynomial can have a zero that is a complex number with a non-zero imaginary part. In fact, complex zeros with non-zero imaginary parts are a common occurrence in polynomials with real coefficients.

Q: How do I know if a zero is a repeated zero?

A: You can determine if a zero is a repeated zero by looking at the multiplicity of the zero. If the zero has a multiplicity greater than 1, then it is a repeated zero.

Q: Can a polynomial have a zero that is a repeated zero?

A: Yes, a polynomial can have a zero that is a repeated zero. In fact, repeated zeros are a common occurrence in polynomials with real coefficients.

Q: How do I find the multiplicity of a zero?

A: To find the multiplicity of a zero, you can use the fact that the multiplicity of a zero is equal to the number of times the factor $(x - r)$ appears in the factorization of the polynomial.

Q: Can a polynomial have a zero that is a complex number with a zero imaginary part?

A: Yes, a polynomial can have a zero that is a complex number with a zero imaginary part. In fact, complex zeros with zero imaginary parts are a common occurrence in polynomials with real coefficients.

Q: How do I know if a zero is a rational zero?

A: You can determine if a zero is a rational zero by looking at the factors of the constant term. If the constant term is a product of integers, then the zero is a rational zero.

Q: Can a polynomial have a zero that is a rational number?

A: Yes, a polynomial can have a zero that is a rational number. In fact, rational zeros are a common occurrence in polynomials with integer coefficients.

Q: How do I find the rational zeros of a polynomial?

A: To find the rational zeros of a polynomial, you can use the fact that the rational zeros are the quotients of the factors of the constant term divided by the factors of the leading coefficient.

Q: Can a polynomial have a zero that is an irrational number?

A: Yes, a polynomial can have a zero that is an irrational number. In fact, irrational zeros are a common occurrence in polynomials with real coefficients.

Q: How do I know if a zero is an irrational number?

A: You can determine if a zero is an irrational number by looking at the decimal representation of the zero. If the decimal representation is non-repeating and non-terminating, then the zero is an irrational number.

Q: Can a polynomial have a zero that is a complex number with a non-zero imaginary part and a non-zero real part?

A: Yes, a polynomial can have a zero that is a complex number with a non-zero imaginary part and a non-zero real part. In fact, complex zeros with non-zero imaginary parts and non-zero real parts are a common occurrence in polynomials with real coefficients.

Q: How do I find the complex zeros of a polynomial?

A: To find the complex zeros of a polynomial, you can use the fact that the complex zeros are the solutions to the equation $P(x) = 0$ , where $P(x)$ is the polynomial.

Q: Can a polynomial have a zero that is a complex number with a zero imaginary part and a non-zero real part?

A: Yes, a polynomial can have a zero that is a complex number with a zero imaginary part and a non-zero real part. In fact, complex zeros with zero imaginary parts and non-zero real parts are a common occurrence in polynomials with real coefficients.

Q: How do I know if a zero is a complex number with a zero imaginary part and a non-zero real part?

A: You can determine if a zero is a complex number with a zero imaginary part and a non-zero real part by looking at the decimal representation of the zero. If the decimal representation is non-repeating and non-terminating, then the zero is a complex number with a non-zero imaginary part and a non-zero real part.

Q: Can a polynomial have a zero that is a complex number with a non-zero imaginary part and a zero real part?

A: Yes, a polynomial can have a zero that is a complex number with a non-zero imaginary part and a zero real part. In fact, complex zeros with non-zero imaginary parts and zero real parts are a common occurrence in polynomials with real coefficients.

Q: How do I find the complex zeros of a polynomial with a non-zero imaginary part and a zero real part?

A: To find the complex zeros of a polynomial with a non-zero imaginary part and a zero real part, you can use the fact that the complex zeros are the solutions to the equation $P(x) = 0$ , where $P(x)$ is the polynomial.

Q: Can a polynomial have a zero that is a complex number with a zero imaginary part and a zero real part?

A: Yes, a polynomial can have a zero that is a complex number with a zero imaginary part and a zero real part. In fact, complex zeros with zero imaginary parts and zero real parts are a common occurrence in polynomials with real coefficients.

Q: How do I know if a zero is a complex number with a zero imaginary part and a zero real part?

A: You can determine if a zero is a complex number with a zero imaginary part and a zero real part by looking at the decimal representation of the zero. If the decimal representation is non-repeating and non-terminating, then the zero is a complex number with a zero imaginary part and a zero real part.

Q: Can a polynomial have a zero that is a complex number with a non-zero imaginary part and a non-zero real part, and also a zero that is a complex number with a zero imaginary part and a zero real part?

A: Yes, a polynomial can have a zero that is a complex number with a non-zero imaginary part and a non-zero real part, and also a zero that is a complex number with a zero imaginary part and a zero real part. In fact, complex zeros with non-zero imaginary parts and non-zero real parts, and complex zeros with zero imaginary parts and zero real parts, are a common occurrence in polynomials with real coefficients.

Q: How do I find the complex zeros of a polynomial with a non-zero imaginary part and a non-zero real part, and also a zero that is a complex number with a zero imaginary part and a zero real part?

A: To find the complex zeros of a polynomial with a non-zero imaginary part and a non-zero real part, and also a zero that is a complex number with a zero imaginary part and a zero real part, you can use the fact that the complex zeros are the solutions to the equation $P(x) = 0$ , where $P(x)$ is the polynomial.

Q: Can a polynomial have a zero that is a complex number with a non-zero imaginary part and a non-zero real part, and also a zero that is a complex number with a zero imaginary part and a zero real part, and also a zero that is a real number?

A: Yes, a polynomial can have a zero that is a complex number with a non-zero imaginary part and a non-zero real part, and also a zero