Let $f(x) = \dfrac{x \ln x - \ln x}{9x^2 - 2e^x x - 9x + 2e^x} + 2$ and $g(x) = \sin^2\left(\dfrac{\pi x^2}{2}\right)$, then the value of $\lim_{x \to 1} \dfrac{f(x)}{g(x)}$ is:
Step-by-Step Solution
Key Concept: L'Hôpital's Rule / Factoring to resolve 0/0 indeterminate forms, then evaluating limits
Step 1: Simplify the numerator of the fraction in $f(x)$.
The numerator is $x\ln x - \ln x = \ln x(x - 1)$.
At $x = 1$, this equals $\ln(1) \cdot (1-1) = 0 \cdot 0 = 0$.
Step 2: Simplify the denominator of the fraction in $f(x)$.
The denominator is:
$$9x^2 - 2e^x x - 9x + 2e^x$$
Rearranging by grouping:
$$9x^2 - 9x - 2e^x x + 2e^x = 9x(x-1) - 2e^x(x-1) = (x-1)(9x - 2e^x)$$
At $x = 1$, this equals $(1-1)(9 - 2e) = 0$.
Step 3: Recognize the indeterminate form and cancel common factors.
Since both numerator and denominator approach $0$ as $x \to 1$, we have a $\dfrac{0}{0}$ indeterminate form. We can cancel the common factor $(x-1)$:
$$f(x) - 2 = \dfrac{\ln x(x-1)}{(x-1)(9x - 2e^x)} = \dfrac{\ln x}{9x - 2e^x}$$
Step 4: Evaluate $f(x)$ at $x = 1$.
$$\lim_{x \to 1} \left(f(x) - 2\right) = \lim_{x \to 1} \dfrac{\ln x}{9x - 2e^x} = \dfrac{\ln 1}{9(1) - 2e^1} = \dfrac{0}{9 - 2e} = 0$$
Therefore:
$$\lim_{x \to 1} f(x) = 2 + 0 = 2$$
Step 5: Evaluate $g(x)$ at $x = 1$.
$$g(1) = \sin^2\left(\dfrac{\pi(1)^2}{2}\right) = \sin^2\left(\dfrac{\pi}{2}\right) = 1^2 = 1$$
Step 6: Calculate the limit of the ratio.
Since $\lim_{x \to 1} f(x) = 2$ and $\lim_{x \to 1} g(x) = 1$, we have:
$$\lim_{x \to 1} \dfrac{f(x)}{g(x)} = \dfrac{2}{1} = 2$$
**Final Answer:** The value of $\lim_{x \to 1} \dfrac{f(x)}{g(x)} = 2$, which corresponds to **Option 1**.
Correct Answer: 4