化简 (a+3)的绝对值+(a-1)的绝对值
分a≤-3,-3≤a≤1,a>1三种情况
a≤-3
(a+3)的绝对值+(a-1)的绝对值
=-a-3-a+1
=-2a-2
-31
(a+3)的绝对值+(a-1)的绝对值
=a+3+a-1
=2a+2