The domain of the function $f(x) = \sin^{–1}\left({|x|+5\over x^2+1}\right)$ is $(–\infty, –a] \cup [a, \infty)$, Then a is equal to :
(1) ${1+\sqrt{17}\over2}$
(2) ${\sqrt{17}-1\over2}$
(3) ${\sqrt{17}\over2}$
(4) ${\sqrt{17}\over2}+1$
(1) ${1+\sqrt{17}\over2}$
(2) ${\sqrt{17}-1\over2}$
(3) ${\sqrt{17}\over2}$
(4) ${\sqrt{17}\over2}+1$