∵△ABC三边分别为a,b,c,
∴ a＜b+c,b＜c+a,c＜a+b
∴a-b-c＜0,b-c-a＜0,c-a-b＜0
则丨a-b-c丨+丨b-c-a丨+丨c-a-b丨
＝[-(a-b-c)]+[-(b-c-a)]+[-(c-a-b)]
=b+c-a+c+a-b+a+b-c
=a+b+c