Math Problem Statement

Degree 3 polynomial with integer coefficients with zeros -3i and (9/7).

Solution

For a degree 3 polynomial with integer coefficients, the given zeros are 3i-3i and 97\frac{9}{7}. Here's how we construct the polynomial step by step:

  1. Use the fact that the coefficients are integers: Since the polynomial has real coefficients, the complex root 3i-3i must have its conjugate 3i3i as a root as well. Therefore, the roots are: 3i, 3i, 97-3i, \ 3i, \ \frac{9}{7}

  2. Form factors from the roots:

    • From the roots 3i-3i and 3i3i, the corresponding factor is: (x+3i)(x3i)=x2+9(x + 3i)(x - 3i) = x^2 + 9
    • From the root 97\frac{9}{7}, the corresponding factor is: (x97)\left( x - \frac{9}{7} \right) To get integer coefficients, multiply by 7 to eliminate the fraction: 7(x97)=7x97 \left( x - \frac{9}{7} \right) = 7x - 9
  3. Form the polynomial: Multiply the factors (x2+9)(x^2 + 9) and (7x9)(7x - 9) to obtain the polynomial: P(x)=(x2+9)(7x9)P(x) = (x^2 + 9)(7x - 9) Expand this expression: P(x)=(x2+9)(7x9)=x2(7x9)+9(7x9)P(x) = (x^2 + 9)(7x - 9) = x^2(7x - 9) + 9(7x - 9) Simplify: P(x)=7x39x2+63x81P(x) = 7x^3 - 9x^2 + 63x - 81

Thus, the degree 3 polynomial with integer coefficients is: P(x)=7x39x2+63x81P(x) = 7x^3 - 9x^2 + 63x - 81

Would you like further explanation, or do you have any questions about the process?

Here are 5 related questions to expand on this concept:

  1. How do complex conjugates affect the formation of polynomials with real coefficients?
  2. Can you derive a polynomial if only two roots (one real, one complex) are given?
  3. What is the relationship between roots and factors of a polynomial?
  4. How would the polynomial change if all the roots were rational numbers?
  5. What if you were asked for a polynomial of degree 4 with one real and one complex root?

Tip: When dealing with polynomials with complex roots, always include the conjugate of the complex root to ensure the coefficients remain real.

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Math Problem Analysis

Mathematical Concepts

Polynomials
Complex Numbers
Rational Roots
Conjugate Roots Theorem

Formulas

(x + 3i)(x - 3i) = x^2 + 9
(x - 9/7) = 7x - 9
P(x) = (x^2 + 9)(7x - 9)

Theorems

Conjugate Roots Theorem
Fundamental Theorem of Algebra

Suitable Grade Level

Grades 11-12