We need to factor the denominator:

x^2 + x - 2

To do so instead of "x" we write "- x + 2x" (since x = 2x - x = -x + 2) and we have

x^2 + x - 2 = x^2 - x + 2x - 2 = (x^2 - x) + (2x - 2) 

We grouped the terms and pull in front "x" and "2" so we have

(x^2 - x) + (2x - 2) =

= x(x - 1) + 2(x - 1) =

= (x - 1)(x + 2)