The value of $\displaystyle\lim_{x \to 0}\left[(1-e^x)\frac{\sin x}{|x|}\right]$ equals:
<b>Note:</b> $[\,\cdot\,]$ denotes the greatest integer function.
Step-by-Step Solution
Key Concept: Greatest integer (floor) function combined with limit evaluation from both sides
Step 1: Identify the function and its behavior near zero.
We need to find $\displaystyle\lim_{x\to 0}\left\lfloor (1-e^x)\frac{\sin x}{|x|}\right\rfloor$, where $\lfloor \cdot \rfloor$ denotes the greatest integer function.
Let us define:
$$g(x) = (1-e^x)\frac{\sin x}{|x|}$$
We will analyze the behavior of $g(x)$ as $x$ approaches $0$ from both sides.
Step 2: Analyze the right-hand limit as $x \to 0^+$.
For $x > 0$, we have $|x| = x$, so:
$$g(x) = (1-e^x)\frac{\sin x}{x}$$
Using standard Taylor expansions near $x = 0$:
- $(1-e^x) \approx -x$ (since $e^x \approx 1 + x$)
- $\frac{\sin x}{x} \approx 1$
Therefore:
$$g(x) \approx (-x) \cdot 1 = -x \to 0^-$$
This means $g(x)$ approaches $0$ from below as $x \to 0^+$.
Step 3: Analyze the left-hand limit as $x \to 0^-$.
For $x < 0$, we have $|x| = -x$, so:
$$g(x) = (1-e^x)\frac{\sin x}{-x} = -(1-e^x)\frac{\sin x}{x}$$
Using Taylor expansions:
- $(1-e^x) \approx -x$ for small $x$
- $\frac{\sin x}{x} \approx 1$
Therefore:
$$g(x) \approx -(-x) \cdot 1 = x$$
Since $x < 0$ in this limit, we have $g(x) \approx x \to 0^-$.
This means $g(x)$ approaches $0$ from below as $x \to 0^-$.
Step 4: Determine the value of the greatest integer function.
From both one-sided limits, we have established that:
$$g(x) \to 0^-$$
This means $g(x)$ approaches $0$ from below, so $g(x)$ takes values in the interval $(-1, 0)$ for $x$ sufficiently close to $0$ (but $x \neq 0$).
For any value $y \in (-1, 0)$, the greatest integer function gives:
$$\lfloor y \rfloor = -1$$
Therefore:
$$\lim_{x \to 0}\left\lfloor (1-e^x)\frac{\sin x}{|x|}\right\rfloor = -1$$
The answer is **Option 2: $-1$**
Correct Answer: 2