MCQ
If $f(x)=\left(25-x^4\right)^{1 / 4}$ for $0 < x<\sqrt{5}$, then $f\left(f\left(\frac{1}{2}\right)\right)=$
  • A
    $2^{-4}$
  • B
    $2^{-3}$
  • C
    $2^{-2}$
  • $2^{-1}$

Answer

Correct option: D.
$2^{-1}$
(D)
Here, $f \left(\frac{1}{2}\right)=\left(25-\frac{1}{16}\right)^{\frac{1}{4}}=\left(\frac{399}{16}\right)^{\frac{1}{4}}$
$\Rightarrow f \left[ f \left(\frac{1}{2}\right)\right]= f \left(\left(\frac{399}{16}\right)^{\frac{1}{4}}\right)$
$=\left(25-\frac{399}{16}\right)^{\frac{1}{4}}$
$=\left(\frac{1}{16}\right)^{\frac{1}{4}}$
$=\frac{1}{2}$

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