1. **State the problem:** We are given the cubic function $$f(x) = 2x^3 - 9x^2 + 7x + 3$$ and need to find its zeros (roots) and any local maximum or minimum values.
2. **Find the zeros:** To find zeros, solve $$f(x) = 0$$:
$$2x^3 - 9x^2 + 7x + 3 = 0$$
3. **Use the Rational Root Theorem and synthetic division or numerical methods:** Testing possible rational roots, we find one root approximately at $$x \approx -0.333$$. Using polynomial division, factor out $$x + 0.333$$ and solve the quadratic remainder:
$$2x^3 - 9x^2 + 7x + 3 = (x + 0.333)(2x^2 - 9.666x + 9)$$
4. **Solve the quadratic:**
Use the quadratic formula:
$$x = \frac{9.666 \pm \sqrt{9.666^2 - 4 \cdot 2 \cdot 9}}{2 \cdot 2}$$
Calculate discriminant:
$$\Delta = 9.666^2 - 72 = 93.44 - 72 = 21.44$$
Square root:
$$\sqrt{21.44} \approx 4.63$$
So,
$$x = \frac{9.666 \pm 4.63}{4}$$
Two roots:
$$x_1 = \frac{9.666 + 4.63}{4} = \frac{14.296}{4} = 3.574$$
$$x_2 = \frac{9.666 - 4.63}{4} = \frac{5.036}{4} = 1.259$$
5. **Zeros in numerical order:**
$$x \approx -0.333, 1.259, 3.574$$
6. **Find local maxima and minima:**
Take the derivative:
$$f'(x) = 6x^2 - 18x + 7$$
Set derivative to zero to find critical points:
$$6x^2 - 18x + 7 = 0$$
Use quadratic formula:
$$x = \frac{18 \pm \sqrt{(-18)^2 - 4 \cdot 6 \cdot 7}}{2 \cdot 6} = \frac{18 \pm \sqrt{324 - 168}}{12} = \frac{18 \pm \sqrt{156}}{12}$$
$$\sqrt{156} \approx 12.49$$
Critical points:
$$x_1 = \frac{18 - 12.49}{12} = \frac{5.51}{12} = 0.459$$
$$x_2 = \frac{18 + 12.49}{12} = \frac{30.49}{12} = 2.541$$
7. **Determine nature of critical points using second derivative:**
$$f''(x) = 12x - 18$$
Evaluate at $$x_1 = 0.459$$:
$$f''(0.459) = 12(0.459) - 18 = 5.508 - 18 = -12.492 < 0$$ so local maximum.
Evaluate at $$x_2 = 2.541$$:
$$f''(2.541) = 12(2.541) - 18 = 30.492 - 18 = 12.492 > 0$$ so local minimum.
8. **Find function values at critical points:**
$$f(0.459) = 2(0.459)^3 - 9(0.459)^2 + 7(0.459) + 3 \approx 3.637$$
$$f(2.541) = 2(2.541)^3 - 9(2.541)^2 + 7(2.541) + 3 \approx -4.637$$
**Final answers:**
- Zeros: $$x \approx -0.333, 1.259, 3.574$$
- Local maximum at $$x \approx 0.459$$ with $$f(x) \approx 3.637$$
- Local minimum at $$x \approx 2.541$$ with $$f(x) \approx -4.637$$
Cubic Zeros Extrema
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