(1)x>=1:f(x)=x-1+x+2>=4,x>=3/2,故有x>=3/2(2)-2<=x<1,f(x)=1-x+x+2=3>=4,不成立.(3)x<-2,f(x)=1-x-(x+2)>=4,x<=5/2,故有x<=-5/2综上所述,解集是x>=3/2或X<=-5/2.
X>=1.5 X< =-2.5
x>=1.5或x<=-2.5
x<=-5/2 x>=3/2
