Question 476459
{{{f(x)=(x-2)/(x-1)}}}
{{{f(s)+f(r)=(s-2)/(s-1)+(r-2)/(r-1)}}}
or we can simplify it 
{{{f(s)+f(r)=(s-2)/(s-1)+(r-2)/(r-1)=((s-2)(r-1)+(r-2)(s-1))/((s-1)(r-1))=(s*r-s-2r+2+s*r-r-2s+2)/((s-1)(r-1))=(2sr-3s-3r+4)/((s-1)(r-1))}}}