Find f'(a).

Question

f(x)= (x^2 + 1)/(x - 2)

So,

[[(a + h)^2 + 1]/[(a + h) - 2]] - [(a^2 + 1)/a - 2] and the whole thing divided by h

I tried simplifying it and ended up with [a + h/-2] - (a-2), which is incorrect. I used wolfram alpha and got (a^2 - 4a - 1)/(a - 2)^2 but I do not know how to get this. Please help.