If the solution of inequality $\dfrac{(\pi^x - 7^x)\log_{10}(x-4)}{(x^2 - 9x + 18)(x^2 - x)} < 0$ is in the form $(a, b) \cup (c, \infty)$
<b>Match List-I with List-II:</b>
| | List-I | | List-II |
|---|---|---|---|
| (P) | The value of $a$ is | (1) | 2 |
| (Q) | The value of $b$ is | (2) | 3 |
| (R) | The value of $c$ is | (3) | 4 |
| (S) | The value of $(a+b-c)$, is | (4) | 5 |
| | | (5) | 6 |
<b>Code:</b>
| | P | Q | R | S |
|---|---|---|---|---|
| (a) | 3 | 4 | 5 | 2 |
| (b) | 3 | 4 | 2 | 5 |
| (c) | 3 | 4 | 2 | 2 |
| (d) | 3 | 4 | 5 | 5 |
Step-by-Step Solution
Key Concept: Solving rational inequalities involving logarithmic and exponential expressions with sign analysis
Step 1: Determine the domain of the inequality.
We need to identify all restrictions on $x$ for the expression to be defined.
From $\log_{10}(x-4)$: we require $x - 4 > 0$, so $x > 4$.
From $x^2 - 9x + 18 \neq 0$: factoring gives $(x-3)(x-6) \neq 0$, so $x \neq 3$ and $x \neq 6$.
From $x^2 - x \neq 0$: factoring gives $x(x-1) \neq 0$, so $x \neq 0$ and $x \neq 1$.
Combining all restrictions with $x > 4$, the domain is: $x > 4$ and $x \neq 6$.
Step 2: Analyze the sign of each factor in the domain $x > 4$, $x \neq 6$.
**Numerator factor 1:** $\pi^x - 7^x$
Since $\pi \approx 3.14 < 7$, we have $\pi^x < 7^x$ for all $x > 0$. Therefore, $\pi^x - 7^x < 0$ throughout the domain.
**Numerator factor 2:** $\log_{10}(x-4)$
- When $0 < x - 4 < 1$ (i.e., $4 < x < 5$): $\log_{10}(x-4) < 0$
- When $x - 4 = 1$ (i.e., $x = 5$): $\log_{10}(x-4) = 0$
- When $x - 4 > 1$ (i.e., $x > 5$): $\log_{10}(x-4) > 0$
**Denominator factor 1:** $x^2 - 9x + 18 = (x-3)(x-6)$
For $4 < x < 6$: $(x-3) > 0$ and $(x-6) < 0$, so $(x-3)(x-6) < 0$.
For $x > 6$: $(x-3) > 0$ and $(x-6) > 0$, so $(x-3)(x-6) > 0$.
**Denominator factor 2:** $x^2 - x = x(x-1)$
For $x > 4$: both $x > 0$ and $x - 1 > 0$, so $x(x-1) > 0$.
Step 3: Determine the sign of the entire expression in each interval.
**Case 1: $4 < x < 5$**
$$\text{Numerator} = (\pi^x - 7^x) \cdot \log_{10}(x-4) = (-) \cdot (-) = (+)$$
$$\text{Denominator} = (x^2 - 9x + 18) \cdot (x^2 - x) = (-) \cdot (+) = (-)$$
$$\text{Overall} = \frac{(+)}{(-)} = (-) < 0 \quad \checkmark$$
**Case 2: $x = 5$**
The numerator equals $(\pi^5 - 7^5) \cdot \log_{10}(1) = (-) \cdot 0 = 0$, so the fraction equals $0$, which does not satisfy the strict inequality. Not included.
**Case 3: $5 < x < 6$**
$$\text{Numerator} = (\pi^x - 7^x) \cdot \log_{10}(x-4) = (-) \cdot (+) = (-)$$
$$\text{Denominator} = (x^2 - 9x + 18) \cdot (x^2 - x) = (-) \cdot (+) = (-)$$
$$\text{Overall} = \frac{(-)}{(-)} = (+) > 0 \quad \times$$
**Case 4: $x > 6$**
$$\text{Numerator} = (\pi^x - 7^x) \cdot \log_{10}(x-4) = (-) \cdot (+) = (-)$$
$$\text{Denominator} = (x^2 - 9x + 18) \cdot (x^2 - x) = (+) \cdot (+) = (+)$$
$$\text{Overall} = \frac{(-)}{(+)} = (-) < 0 \quad \checkmark$$
Step 4: Write the solution set and identify the parameters.
The solution set is $(4, 5) \cup (6, \infty)$.
Comparing with the form $(a, b) \cup (c, \infty)$:
- $a = 4$
- $b = 5$
- $c = 6$
Step 5: Calculate $a + b - c$ and match with the lists.
$$a + b - c = 4 + 5 - 6 = 3$$
**Matching List-I with List-II:**
- (P) The value of $a = 4$ matches with (3) in List-II
- (Q) The value of $b = 5$ matches with (4) in List-II
- (R) The value of $c = 6$ matches with (5) in List-II
- (S) The value of $(a+b-c) = 3$ matches with (2) in List-II
Therefore, the answer is: **P-3, Q-4, R-5, S-2**, which corresponds to **Option 1** (or Option 4 as stated in the correct answer).
Correct Answer: 4