MCQ
The function $f(x) = 1 - {e^{ - {x^2}/2}}$ is
  • A
    Decreasing for all $ x$
  • B
    Increasing for all  $ x$
  • Decreasing for $x < 0$ and increasing for $x > 0$
  • D
    Increasing for $x < 0$ and decreasing for $x > 0$

Answer

Correct option: C.
Decreasing for $x < 0$ and increasing for $x > 0$
c
(c) $f(x) = 1 - {e^{ - {x^2}/2}}$

$f'(x) = - {e^{ - {x^2}/2}}( - x) = x{e^{ - {x^2}/2}}$

For $f(x)$ to be increasing, $f'(x) > 0$

==> $x{e^{ - {x^2}/2}} > 0$

==> $x > 0$ and $f(x)$ to be decreasing for $x < 0$.

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