Q82 / 150 · MHT CET 2025 (19 Apr Shift 2) · Mathematics
If $\mathrm{f}(x)=\frac{(27-2 x)^{\frac{1}{3}}-3}{9-3(243+5 x)^{\frac{1}{5}}}, x \neq 0$ is continuous at $x=0$, then the value of $f(0)$ is
- A$\frac{2}{3}$
- B$6$
- Correct answerC$2$
- D$\frac{1}{3}$
Solution
To ensure continuity at $x=0$, define $f(0) = \lim_{x \to 0} f(x)$ where
$f(x)=\frac{(27-2 x)^{\frac{1}{3}}-3}{9-3(243+5 x)^{\frac{1}{5}}}$.
Direct substitution yields the indeterminate form $\frac{0}{0}$, requiring further analysis.
Applying L'Hôpital's rule, differentiate numerator and denominator:
$N'(x) = -\frac{2}{3}(27-2x)^{-\frac{2}{3}}$
$D'(x) = -3(243+5x)^{-\frac{4}{5}}$
The limit becomes
$\lim_{x \to 0} \frac{N'(x)}{D'(x)} = \frac{-\frac{2}{3}(27)^{-\frac{2}{3}}}{-3(243)^{-\frac{4}{5}}}$.
Expressing $27=3^3$ and $243=3^5$, we simplify:
$\frac{-\frac{2}{3} \cdot 3^{-2}}{-3 \cdot 3^{-4}} = \frac{-\frac{2}{27}}{-\frac{1}{27}} = 2$.
Alternatively, using the standard limit $\lim_{y \to 0} \frac{(a+y)^n - a^n}{y} = n a^{n-1}$, we compute numerator and denominator limits separately.
The numerator limit transforms to $-2 \cdot \frac{1}{3}(27)^{-\frac{2}{3}} = -\frac{2}{27}$.
The denominator limit becomes $-15 \cdot \frac{1}{5}(243)^{-\frac{4}{5}} = -\frac{1}{27}$.
The ratio confirms $\lim_{x \to 0} f(x) = 2$.
Final answer: $f(0) = 2$
Hence, the correct answer is option: 'C'.