已知-1
因为-1
a>-1则a+1>0则|a+1|=a+1a<3则a-3<0则|a-3|=3-a那么|a+1|+|a-3|=a+1+3-a=4
a+1大于0 a-3小于0 所以|a+1|+|a-3|=a+1+3-a=4