\(\frac{d}{{dx}}({\sinh ^{ - 1}}x)\) is equal to _____: \(\frac{1}{{\sqrt {1 - {x^2}} }}\) \(\frac{{ - 1}}{{\sqrt {1 - {x^2}} }}\) \(\frac{1}{{\sqrt {1 + {x^2}} }}\) \(\frac{1}{{\sqrt {1 + {x^2}} }}\)