Let f(x) = (x + 1)/(x - 1). What is f(f(2010))?
I'll do this the bash way
f(2010) = (2011)/(2009)
f(2011/2009) = (4020/2009)/(2/2009) = 4020/2009 * 2009/2 = 2010
You can also notice that f[(x+1)/(x-1)] = x
