Question Details

The function f(x) = e∣ˣ∣ is

Options

A

continuous everywhere but not differentiable at x = 0

B

continuous and differentiable everywhere

C

not continuous at x = 0

D

None of these

Correct Answer :

continuous everywhere but not differentiable at x = 0

Solution :

The correct option is: "continuous everywhere but not differentiable at x = 0".

To understand why this is correct, let us analyze the continuity and differentiability of the function:
f ( x ) = e | x |
Recall that the absolute value function is defined piecewise as:
| x | = { x if x 0 x if x < 0
Therefore, we can rewrite the function f(x) piecewise as:
f ( x ) = { e x if x 0 e x if x < 0

Step 1: Check Continuity everywhere
For x>0, f(x)=ex, which is an exponential function and is continuous.
For x<0, f(x)=ex, which is also an exponential function and is continuous.
Now, we check the continuity at the transition point x=0:
1. Left-Hand Limit (LHL) as x0:
lim x 0 f ( x ) = lim x 0 e x = e 0 = 1
2. Right-Hand Limit (RHL) as x0+:
lim x 0 + f ( x ) = lim x 0 + e x = e 0 = 1
3. Function value at x=0:
f ( 0 ) = e | 0 | = e 0 = 1
Since LHL=RHL=f(0)=1, the function f(x) is continuous at x=0. Thus, f(x) is continuous everywhere.

Step 2: Check Differentiability at x = 0
To determine differentiability at x=0, we calculate the Left-Hand Derivative (LHD) and Right-Hand Derivative (RHD) at this point:
1. Left-Hand Derivative (LHD) at x=0:
LHD = lim h 0 f ( 0 + h ) f ( 0 ) h = lim h 0 e h 1 h
Using the standard limit limu0eu1u=1, let u=h:
LHD = lim h 0 e h 1 h = ( 1 ) = 1
2. Right-Hand Derivative (RHD) at x=0:
RHD = lim h 0 + f ( 0 + h ) f ( 0 ) h = lim h 0 + e h 1 h = 1
Since LHD=1 and RHD=1, we have:
LHD RHD
Thus, the function is not differentiable at x=0 (geometrically, the graph of e|x| has a sharp corner or "V-shape" at x=0).

Conclusion
The function f(x)=e|x| is continuous everywhere but is not differentiable at x=0.

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