回复：借地儿问道题

1/(x^2 + x - 2) = 1 / [(x-1)(x+2)] = [1/(x-1) - 1/(x+2)]/3 

integral of the above expression is (1/3) * ln [(x-1)/(x+2)]

so the answer is -(1/3) * ln 4

(original problem should not have dx twice)