Consider the following statements regarding the function f(x) = |ln x| − |x − 1|
Statement 1: f(x) is differentiable for all x > 0
Statement 2: f(x) is increasing in (1, ∞)
Statement 3: f(x) is decreasing in (0, 1)
Correct Answer :
Statement 1 and statement 3 are true
Solution :
We are given the function:
defined for .
Let's analyze the behaviors of the logarithmic term and the linear term on different intervals.
Case 1: When
For , we have and .
Thus, the absolute values can be opened directly:
Case 2: When
For , we have and .
Thus, the absolute values open with negative signs:
Now we evaluate each statement step-by-step.
Evaluating Statement 1: Differentiability at
Since is composed of differentiable functions in the intervals and , we only need to check differentiability at the boundary point .
Let us find the left-hand derivative (LHD) and right-hand derivative (RHD) at .
For :
Taking the limit as :
For :
Taking the limit as :
Since the Left-Hand Derivative equals the Right-Hand Derivative () at , the function is differentiable at . Since it is differentiable everywhere else in , Statement 1 is true.
Evaluating Statement 2: Monotonicity in
For , we have:
Since , we have , which implies:
Therefore, is decreasing in . Thus, Statement 2 is false.
Evaluating Statement 3: Monotonicity in
For , we have:
Since , we have , which implies:
Thus, for all .
Therefore, is decreasing in . Thus, Statement 3 is true.
Consequently, Statement 1 and Statement 3 are true, while Statement 2 is false.
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