Let $f(x) = x^2+\frac{250}{x}$ be any function defined on $R - \{0\}$, where $R$ is the set of real numbers. Then which of the following are TRUE? (A) $f'(x) = 2x +\frac{250}{x^2}$ Choose the correct answer from the options given below: |
(A) and (B) only (B) and (C) only (C) and (D) only (A), (B) and (D) only |
(B) and (C) only |
The correct answer is Option (2) → (B) and (C) only Given function: $f(x) = x^2 + \frac{250}{x}$, defined on $\mathbb{R} - \{0\}$. Differentiate: $f'(x) = 2x - \frac{250}{x^2}$ Hence, (A) $f'(x) = 2x + \frac{250}{x^2}$ is false. Find critical points: $f'(x) = 0 \Rightarrow 2x - \frac{250}{x^2} = 0$ $\Rightarrow 2x^3 = 250 \Rightarrow x^3 = 125 \Rightarrow x = 5$ Thus, (B) is true. Second derivative: $f''(x) = 2 + \frac{500}{x^3}$ At $x = 5$, $f''(5) = 2 + \frac{500}{125} = 6 > 0$, hence minimum at $x = 5$. Minimum value: $f(5) = 5^2 + \frac{250}{5} = 25 + 50 = 75$ So, (C) is true. As $x \to 0$, $\frac{250}{x} \to \infty$ or $-\infty$ depending on sign of $x$, and as $x \to \infty$, $f(x) \to \infty$. Therefore, there is no maximum value. (D) is false. Correct statements: (B) and (C) |