Function Analysis F240E5
1. **Problem statement:** Given the function $y = f(x) = ax^3 + bx^2 + cx + d$ with the derivative sign table and function behavior:
- $f'(x)$ changes sign: positive on $(-\infty, -1)$, zero at $x=-1$, negative on $(-1, 2)$, zero at $x=2$, positive on $(2, +\infty)$.
- $f(x)$ increases from $-\infty$ to 1 at $x=-1$, then decreases to $-2$ at $x=2$, then increases to $+\infty$.
We analyze the statements:
a) The function has a local minimum at $x=2$.
b) The function is decreasing on $(0,1)$.
c) On $(-\infty, 2)$, the function's maximum is 1 and minimum is $-2$.
Also, the function $y = \frac{2024}{f'(x) + 1}$ has 4 asymptotes.
2. **Key formulas and rules:**
- Critical points occur where $f'(x) = 0$.
- If $f'(x)$ changes from negative to positive at a point, $f$ has a local minimum there.
- If $f'(x)$ changes from positive to negative, $f$ has a local maximum.
- A function is decreasing where $f'(x) < 0$.
- The maximum and minimum values on an interval can be found at critical points or endpoints.
- Vertical asymptotes of $y = \frac{2024}{f'(x) + 1}$ occur where $f'(x) + 1 = 0$, i.e., $f'(x) = -1$.
3. **Step-by-step analysis:**
**a) Local minimum at $x=2$?**
- From the table, $f'(x)$ changes from negative (on $( -1, 2)$) to zero at $x=2$, then positive on $(2, +\infty)$.
- This sign change from negative to positive means $f$ has a local minimum at $x=2$.
- The statement is **true**.
**b) Is $f$ decreasing on $(0,1)$?**
- On $( -1, 2)$, $f'(x) < 0$, so $f$ is decreasing on the entire interval $( -1, 2)$.
- Since $(0,1) \subset (-1,2)$, $f$ is decreasing on $(0,1)$.
- The statement is **true**.
**c) Maximum and minimum on $(-\infty, 2)$?**
- On $(-\infty, -1)$, $f'(x) > 0$, so $f$ is increasing.
- At $x=-1$, $f'(x)=0$, $f(x)=1$ (local max).
- On $(-1, 2)$, $f'(x) < 0$, so $f$ is decreasing.
- At $x=2$, $f'(x)=0$, $f(x)=-2$ (local min).
- So on $(-\infty, 2)$, the maximum is $1$ at $x=-1$ and minimum is $-2$ at $x=2$.
- The statement is **true**.
**d) Number of asymptotes of $y = \frac{2024}{f'(x) + 1}$?**
- Vertical asymptotes occur where denominator is zero: $f'(x) + 1 = 0 \Rightarrow f'(x) = -1$.
- Since $f'(x)$ is a quadratic (derivative of cubic), it can equal $-1$ at up to 2 points.
- However, the problem states there are 4 asymptotes, implying $f'(x) + 1$ has 4 zeros or the function has other asymptotes (horizontal or oblique).
- Without explicit $f'(x)$, we cannot confirm 4 vertical asymptotes.
4. **Summary:**
- a) True
- b) True
- c) True
- d) Cannot confirm with given data
**Final answer:**
- a), b), c) are correct.