1. **Stating the problem:** We are given the cubic polynomial $x^3 - 2x^2 + 2kx + 8$ and need to analyze or solve it depending on the context (e.g., find roots, factor, or determine $k$ for certain conditions).
2. **Formula and rules:** For cubic polynomials of the form $ax^3 + bx^2 + cx + d$, the roots can be found using factoring, synthetic division, or the cubic formula. Important rules include the Rational Root Theorem and the factor theorem.
3. **Intermediate work:** To find roots or factor, we can try possible rational roots using factors of the constant term 8: $\pm1, \pm2, \pm4, \pm8$.
4. **Testing $x= -2$:** Substitute $x = -2$:
$$(-2)^3 - 2(-2)^2 + 2k(-2) + 8 = -8 - 8 - 4k + 8 = -8 - 4k$$
For $x = -2$ to be a root, set equal to zero:
$$-8 - 4k = 0 \implies 4k = -8 \implies k = -2$$
5. **With $k = -2$, the polynomial becomes:**
$$x^3 - 2x^2 - 4x + 8$$
6. **Factor by synthetic division using root $x = -2$:**
Divide $x^3 - 2x^2 - 4x + 8$ by $(x + 2)$:
Coefficients: 1, -2, -4, 8
Bring down 1, multiply by -2: -2, add to -2: -4
Multiply -4 by -2: 8, add to -4: 4
Multiply 4 by -2: -8, add to 8: 0 (remainder)
Quotient: $x^2 - 4x + 4$
7. **Factor quotient:**
$$x^2 - 4x + 4 = (x - 2)^2$$
8. **Final factorization:**
$$x^3 - 2x^2 - 4x + 8 = (x + 2)(x - 2)^2$$
9. **Roots:**
$$x = -2, 2 \text{ (double root)}$$
**Answer:** For $k = -2$, the polynomial factors as $(x + 2)(x - 2)^2$ with roots $-2$ and $2$ (double root).
Cubic Polynomial 7F2949
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