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,则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 --|||-,