1/(x^4-x^2) = -1/x^2 - 1/[2 (x+1)] + 1/[2 (x-1)]
积分 =1/x + (1/2) ln(1 - x) - (1/2) ln(1 + x) +C
如果要写短些
1/x - arctanhx +C (保证是对的,但不推荐,有可能被打叉)