If \(f\left( x \right) = \sqrt {25 - {x^2},} \) then what is \(\mathop {\lim }\limits_{x \to 1} \frac{{f\left( x \right) - f\left( 1 \right)}}{{x - 1}}\) equal to?
1
\( - \frac{1}{{\sqrt {24} }}\)
2
\(\frac{1}{{\sqrt {24} }}\)
3
\( - \frac{1}{{4\sqrt 3 }}\)
4
\(\frac{1}{{4\sqrt 3 }}\)