Local Extrema 6Ea8A9
1. **Problem Statement:** Find the local maximum and minimum values of the function $$y = x^5 - 5x^4 + 5x^3 - 10$$.
2. **Formula and Rules:** To find local maxima and minima, we use the first derivative test.
- Find the first derivative $$y' = \frac{dy}{dx}$$.
- Solve $$y' = 0$$ to find critical points.
- Use the second derivative $$y''$$ to determine the nature of each critical point:
- If $$y''(x) > 0$$, local minimum.
- If $$y''(x) < 0$$, local maximum.
3. **Find the first derivative:**
$$y = x^5 - 5x^4 + 5x^3 - 10$$
$$y' = 5x^4 - 20x^3 + 15x^2$$
4. **Factor the first derivative:**
$$y' = 5x^2(x^2 - 4x + 3)$$
Factor quadratic:
$$x^2 - 4x + 3 = (x - 1)(x - 3)$$
So,
$$y' = 5x^2 (x - 1)(x - 3)$$
5. **Find critical points by setting $$y' = 0$$:**
$$5x^2 (x - 1)(x - 3) = 0$$
Critical points are $$x = 0, 1, 3$$.
6. **Find the second derivative:**
$$y' = 5x^4 - 20x^3 + 15x^2$$
$$y'' = 20x^3 - 60x^2 + 30x$$
7. **Evaluate $$y''$$ at each critical point:**
- At $$x=0$$:
$$y''(0) = 0$$ (inconclusive, test with first derivative sign change)
- At $$x=1$$:
$$y''(1) = 20(1)^3 - 60(1)^2 + 30(1) = 20 - 60 + 30 = -10 < 0$$ (local maximum)
- At $$x=3$$:
$$y''(3) = 20(27) - 60(9) + 30(3) = 540 - 540 + 90 = 90 > 0$$ (local minimum)
8. **Check behavior at $$x=0$$:**
Test values around 0 in $$y'$$:
- For $$x = -0.1$$, $$y' > 0$$
- For $$x = 0.1$$, $$y' > 0$$
No sign change, so no local extremum at $$x=0$$.
9. **Find function values at critical points:**
- $$y(1) = 1 - 5 + 5 - 10 = -9$$
- $$y(3) = 243 - 405 + 135 - 10 = (243 - 405) + 125 = -162 + 125 = -37$$
10. **Final answer:**
- Local maximum at $$x=1$$ with value $$y = -9$$.
- Local minimum at $$x=3$$ with value $$y = -37$$.