Q. If $f (x) = ∣ cos x ∣$ then $f^{1} (\frac{π}{4})$ is

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A

$\frac{1}{2}$

B

$\frac{- 1}{2}$

C

0

D

Not exist

Solution:

$f (x) = ∣ cos x ∣ = cos x$ ,
if $0 < x < \frac{π}{2}$
$f^{1} (x) = - sin x$
$f^{1} (\frac{π}{4}) = \frac{- 1}{2}$