According to the known conditions, A, B and C are three sides of a triangle, which satisfies the conditions. Any two sides are larger than the third side, so the simplification is as follows:
a-b-c & lt; 0,a-b+ c & lt; 0,a+b-c & gt; 0;
-(a-b-c)-(a-b+c)+a+b-c =-a+b+c-a+b-c+a+B- c = 3 B- a-c