If
f(x)=xcosh1(x3)x29\displaystyle {f{{\left({x}\right)}}}={x}{{\cosh}^{{-{1}}}{\left({\frac{{{x}}}{{{3}}}}\right)}}-\sqrt{{{x}^{{2}}-{9}}}
then f(9)=\displaystyle {f}'{\left({9}\right)}=   .