1、x - 1 是分子分母的公因子 common factor,可以约分 cancel each other,并不影响极限值。.2、但是 x = 1 时,分母变成了0,所以,x = 1 是属于 可去型间断点 removable discontinuity / singularity。.3、x = 2,左极限是负无穷大,右极限是正无穷大, 所以,x = 2 是无穷型间断点 infinite discontinuity / singularity,essential discontinuity / singularity。..