5. Find a polynomial with integer coefficients that has degree 3 and zeros 5, and 2i. [Multiply out to write this polynomial in standard form]

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**Problem 5: Polynomial Construction**

*Objective:* Find a polynomial with integer coefficients that has degree 3 and zeros 5, and \(2i\). Multiply out to write this polynomial in standard form.

\[ \text{_______________________________} \]

**Instructions:**
1. Recall that complex zeros occur in conjugate pairs if the polynomial has real coefficients. Thus, if \(2i\) is a zero, then \(-2i\) must also be a zero.
2. Identify the zeros of the polynomial: \(5\), \(2i\), and \(-2i\).
3. Construct factors from the zeros:
   - For the zero 5: \( (x - 5) \)
   - For the zero \(2i\): \( (x - 2i) \)
   - For the zero \(-2i\): \( (x + 2i) \)
4. Multiply the factors to construct the polynomial:
   \[
   (x - 5)(x - 2i)(x + 2i)
   \]
5. Simplify the expression:
   - First, multiply the complex conjugate pair: 
   \[
   (x - 2i)(x + 2i) = x^2 - (2i)^2 = x^2 + 4
   \]
   - Next, multiply by the remaining factor:
   \[
   (x - 5)(x^2 + 4) = x(x^2 + 4) - 5(x^2 + 4)
   \]
   - Distribute and combine like terms:
   \[
   x^3 + 4x - 5x^2 - 20 = x^3 - 5x^2 + 4x - 20
   \]

The polynomial in standard form is:
\[ x^3 - 5x^2 + 4x - 20 \]
Transcribed Image Text:**Problem 5: Polynomial Construction** *Objective:* Find a polynomial with integer coefficients that has degree 3 and zeros 5, and \(2i\). Multiply out to write this polynomial in standard form. \[ \text{_______________________________} \] **Instructions:** 1. Recall that complex zeros occur in conjugate pairs if the polynomial has real coefficients. Thus, if \(2i\) is a zero, then \(-2i\) must also be a zero. 2. Identify the zeros of the polynomial: \(5\), \(2i\), and \(-2i\). 3. Construct factors from the zeros: - For the zero 5: \( (x - 5) \) - For the zero \(2i\): \( (x - 2i) \) - For the zero \(-2i\): \( (x + 2i) \) 4. Multiply the factors to construct the polynomial: \[ (x - 5)(x - 2i)(x + 2i) \] 5. Simplify the expression: - First, multiply the complex conjugate pair: \[ (x - 2i)(x + 2i) = x^2 - (2i)^2 = x^2 + 4 \] - Next, multiply by the remaining factor: \[ (x - 5)(x^2 + 4) = x(x^2 + 4) - 5(x^2 + 4) \] - Distribute and combine like terms: \[ x^3 + 4x - 5x^2 - 20 = x^3 - 5x^2 + 4x - 20 \] The polynomial in standard form is: \[ x^3 - 5x^2 + 4x - 20 \]
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