Question 824672
Did you mean {{{f(x)=3/(x-1)}}} or {{{f(x)=3/x-1}}}  ?
They are not the same.  


Whichever is the function you want, "find the function value" means replace x in the function expression with the specified value, and COMPUTE what this value is.  Simple substitution and then computation.


What if you wanted, f(21)?
Is your function, {{{3/(x-1)}}}?
'
{{{3/(21-1)}}}
{{{3/20}}}, and that's it.


Taking another look at your description, did you mean, {{{f(x)=3*sqrt(1/(x-1))}}}?