Let <span class="math-inline">f(x) = [x - 1] + \{x\}^{[x]}, x \in (1,3)</span>, then <span class="math-inline">f^{-1}(x)</span> is -
(A) \frac{x + 1}{2 + \sqrt{x - 1}} \quad x \in (1,2)
(B) \frac{x - 1}{2 - \sqrt{x - 1}} \quad x \in (2,3)
(C) \frac{x - 1}{2 - \sqrt{x - 1}} \quad x \in (0,1)
(D) \frac{x + 1}{2 + \sqrt{x - 1}} \quad x \in (1,2)
Step-by-Step Solution
Key Concept: We need to analyze f(x) by breaking the domain (1,3) into intervals where [x] and {x} have constant behavior, then find the inverse by solving y = f(x) for x in each interval.
Step 1: Analyze $f(x)$ on interval $(1,2)$
For $x \in (1,2)$, we have:
$[x-1] = 0$ (since $0 < x-1 < 1$)
$[x] = 1$
$\{x\} = x-1$
Substitute these into the definition of $f(x) = [x-1] + \{x\}^{[x]}$:
$$f(x) = 0 + (x-1)^1 = x-1$$
The range of $f(x)$ for $x \in (1,2)$ is $(0,1)$.
Step 2: Find $f^{-1}(x)$ for $x \in (0,1)$
Let $y = f(x)$. From Step 1, we have $y = x-1$.
Solving for $x$ in terms of $y$:
$$x = y+1$$
Thus, the inverse function is $f^{-1}(y) = y+1$. Replacing $y$ with $x$, we obtain:
$$f^{-1}(x) = x+1 \quad \text{for } x \in (0,1)$$
Step 3: Analyze $f(x)$ on interval $(2,3)$
For $x \in (2,3)$, we have:
$[x-1] = 1$ (since $1 < x-1 < 2$)
$[x] = 2$
$\{x\} = x-2$
Substitute these into the definition of $f(x) = [x-1] + \{x\}^{[x]}$:
$$f(x) = 1 + (x-2)^2$$
To find the range of $f(x)$ for $x \in (2,3)$:
As $x \to 2^+$, $f(x) \to 1 + (2-2)^2 = 1$.
As $x \to 3^-$, $f(x) \to 1 + (3-2)^2 = 1+1 = 2$.
So the range of $f(x)$ for $x \in (2,3)$ is $[1,2)$.
Step 4: Find $f^{-1}(x)$ for $x \in [1,2)$
Let $y = f(x)$. From Step 3, we have $y = 1 + (x-2)^2$.
Rearranging the equation:
$$y-1 = (x-2)^2$$
Since $x \in (2,3)$, $x-2$ is positive. Therefore, we take the positive square root:
$$x-2 = \sqrt{y-1}$$
Solving for $x$ in terms of $y$:
$$x = 2 + \sqrt{y-1}$$
Thus, the inverse function is $f^{-1}(y) = 2 + \sqrt{y-1}$. Replacing $y$ with $x$, we obtain:
$$f^{-1}(x) = 2 + \sqrt{x-1} \quad \text{for } x \in [1,2)$$
Combining the results from Step 2 and Step 4, the inverse function $f^{-1}(x)$ is defined piecewise as:
$$f^{-1}(x) = \begin{cases} x+1 & \text{for } x \in (0,1) \\ 2 + \sqrt{x-1} & \text{for } x \in [1,2) \end{cases}$$
Correct Answer: A