Assume that $f$ is continuous on $[a, b]$, $a > 0$ and differentiable on $(a, b)$. If $\dfrac{f(a)}{a} = \dfrac{f(b)}{b}$, then there exists $x_0 \in (a, b)$ such that:
Step-by-Step Solution
Key Concept: Rolle's theorem applied to auxiliary function
Step 1: Define an auxiliary function to apply Rolle's theorem.
We define $g(x) = \frac{f(x)}{x}$. Since $a > 0$, the function $g$ is well-defined on the interval $[a, b]$.
Step 2: Verify that the auxiliary function satisfies the conditions of Rolle's theorem.
Since $f$ is continuous on $[a, b]$ and differentiable on $(a, b)$, and since $x > 0$ on this interval, the function $g(x) = \frac{f(x)}{x}$ is also continuous on $[a, b]$ and differentiable on $(a, b)$.
Step 3: Check the boundary condition for Rolle's theorem.
We are given that $\dfrac{f(a)}{a} = \dfrac{f(b)}{b}$. This means:
$$g(a) = g(b)$$
Step 4: Apply Rolle's theorem.
Since $g$ is continuous on $[a, b]$, differentiable on $(a, b)$, and $g(a) = g(b)$, by Rolle's theorem, there exists at least one point $x_0 \in (a, b)$ such that:
$$g'(x_0) = 0$$
Step 5: Compute the derivative of $g(x)$ and evaluate at $x_0$.
Using the quotient rule:
$$g'(x) = \frac{d}{dx}\left(\frac{f(x)}{x}\right) = \frac{x \cdot f'(x) - f(x) \cdot 1}{x^2} = \frac{xf'(x) - f(x)}{x^2}$$
Setting $g'(x_0) = 0$:
$$\frac{x_0 f'(x_0) - f(x_0)}{x_0^2} = 0$$
Since $x_0 > 0$, we have $x_0^2 \neq 0$, so the numerator must equal zero:
$$x_0 f'(x_0) - f(x_0) = 0$$
Therefore:
$$x_0 f'(x_0) = f(x_0)$$
**Final Answer:** There exists $x_0 \in (a, b)$ such that $x_0 f'(x_0) = f(x_0)$, which corresponds to **Option 1**.
Correct Answer: 1