Here is the procedure which might help).
procedure sqrt2(var strAnswer:string; var Expon:integer; strNum1: string; NumPlaces:integer);
var
a,b: MPFloat;
n:integer;
p:mp_exp_t;
begin
f_init (a);
f_init (b);
f_set_str (a, '1', 10);
f_set_str (b, strNum1, 10);
p:=4*NumPlaces;
f_set_prec (a, p);
f_sqrt (a,b);
strAnswer:=f_get_str(n, 10, p, a);
Expon:=n;
f_clear (a);
f_clear (b);
end;