f(x)=|x+3|+|x-1|f(x)=-x-3+1-x=-2x-2 x<-3f(x)=x+3+1-x=4 -3≤x≤1f(x)=x+3+x-1=2x+2 x>1∴最小值m=4f(a)=m→a∈[-3,1]
