If f: R→R is defined by f(x) = (4-x^2)^1/2, then fof(x) is :

The correct answer is Option (1) → $|x|$

$f(x)=(4-x^2)^{\frac{1}{2}}$

So $fof(x)=\left(4-\left(\left(4-x^2\right))^{\frac{1}{2}}\right)^2\right)^{\frac{1}{2}}$

$=\left(4-4+x^2\right)^{\frac{1}{2}}$

$=|x|$