因为 a,b,c为三角形ABC的三边边长 所以 a + b > c ,b + c > a ,a + c > b 所以 a - b - c < 0 ,b - c - a < 0 ,c - a - b < 0 所以 |a - b - c| + |b - c - a| + |c - a - b| = b + c - a + a + c - b + a + b - c = a + b + c
∵ a,b,c为△ABC的三边的长 ∴ a + b > c , b + c > a , a + c > b ∴a - b - c < 0 , b - c - a < 0 , c - a - b < 0 ∴ |a - b - c| + |b - c - a| + |c - a - b| = b + c - a + a + c - b + a + b - c = a + b + c