Theo đầu bài ta có:
\(\left(a+b-c\right)+\left(a-b+c\right)-\left(b+c-a\right)-\left(a-b-c\right)\)
\(=a+b-c+a-b+c-b-c+a-a+b+c\)
\(=\left(a+a+a-a\right)+\left(b-b-b+b\right)+\left(c-c-c+c\right)\)
\(=2a\)
(a+b-c) + (a-b+c) - (b+c-a) - (a-b-c)
= a + b - c + a - b + c - b - c + a - a + b + c
= 2a
(a+b-c)+(a-b+c)-(b+c-a)-(a-b-c)=a+b-c+a-b+c-b-c+a-a+b+c=(a+a+a-a)+(b-b-b+b)+(-c+c-c+c)
=2a+ 0 + 0
=2a