3.下列函数在指出的点处间断,说明这些间断点属于哪一类.如果是可去间断点,-|||-那么补充或改变函数的定义使它连续:-|||-(1) =dfrac ({x)^2-1}({x)^2-3x+2} x=1 x=2 :-|||-(2) =dfrac (x)(tan x) =kpi =kpi +dfrac (pi )(2)(k=0,pm 1,pm 2,... ) ;-|||-(3) =(cos )^2dfrac (1)(x),x=0 =-|||-,-|||-(4) y= ) x-1,xleqslant 1 3-x,xgt 1 . .x=1 --|||-,