Question 15

Mathematics Continuous function Hard

The function $$ f(x) = \begin{cases} (1 + 2x)^{1/x}, & \text{for } x \ne 0 \\ e^2, & \text{for } x = 0 \end{cases} $$ is

(A) Differentiable at x = 0
(B) Continuous at x = 0
(C) Discontinuous at x = 0
(D) Not differentiable at x = 0
✓ Correct Answer: Option E Verified Solution

📘 Step-by-Step Solution & Detailed Explanation:

Using the result \[ \lim_{x \to 0} (1 + kx)^{\frac{1}{x}} = e^k, \] the value of the function \( f(x) = (1 + 2x)^{\frac{1}{x}} \) as \( x \to 0 \) is: \[ e^2. \] Also, given that \( f(0) = e^2 \), to check the differentiability of the function, let: \[ y = (1 + 2x)^{\frac{1}{x}} \Rightarrow \log y = \frac{1}{x} \log(1 + 2x). \] \[ \Rightarrow \log y = \frac{1}{x} \left( 2x - \frac{4x^2}{2} + \ldots \right) = 2 - 2x + \ldots. \] Hence, \[ y = e^{2 - 2x + \ldots} = e^2 e^{-2x + \ldots} = e^2(1 - 2x + \ldots). \] Now, the right-hand derivative: \[ \frac{f(0+h) - f(0)}{h} = \frac{e^2(1 - 2h + \ldots) - e^2}{h} = -2e^2. \] Similarly, we can show that the left-hand derivative is also \( -2e^2 \). Therefore, the function is differentiable at \( x = 0 \).

Practice Similar Continuous function Questions

Reinforce your conceptual grasp with related questions from NIMCET 2022:

Q23 \(f(x)=x+|x|\) is continuous for
Solve →
Q1 Inverse of the function \(f(x)= 10 x-10 -x 10 x +10 -x \) is
Solve →
Q2 Let \( a , b , c \) be distinct non-negative numbers. If the vectors \(a i...
Solve →
Q3 The correct expression for \(cos -1 (-x)\) is
Solve →
Q4 Suppose that the temperature at a point (x,y), on a metal plate is...
Solve →
Full-Length Test Series

Prepare for NIMCET Under Real Exam Conditions

Take timed full-length mock tests with authentic question distributions, negative marking (+12/-3 in Math), and instant All India Rank calculation.

Start Free Mock Test Series →