MCQ
Function $f(x) = |x| - |x - 1|$ is monotonically increasing when:
  • A
    $x < 0$
  • B
    $x > 1$
  • C
    $x < 1$
  • $0 < x < 1$

Answer

Correct option: D.
$0 < x < 1$
$f(x) = |x| - |x - 1|$
Case $I:$
Let $x < 0$
If $x < 0,$ then $|x| = -x$
$\Rightarrow |x - 1| = -(x - 1)$
Now,
$f(x) = |x| - |x - 1|$
$= -x - (-x + 1)$
$= -x + x - 1$
$= -1$
$f'(x) = 0$
So, $f(x)$ is not monotonically increasing when $x < 0.$
Case $II:$
Let $x < 0 < 1$
Here,
$|x| = x$
$\Rightarrow |x - 1| = -(x - 1)$
Now,
$f(x) = |x| - |x - 1|$
$= x + x -1$
$= 2x - 1$

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