a等于0的话积分不就变成∫ 1/x² dx咯,不是∫ dx/(x² - a²)的形式
∫ dx/(x² - a²)
= (1/2a)∫ [(x + a) - (x - a)]/[(x - a)(x + a)] dx
= (1/2a)∫ [1/(x - a) - 1/(x + a)] dx
= (1/2a)(ln|x - a| - ln|x + a|) + C
= (1/2a)ln|(x - a)/(x + a)| + C