The relationship between ABC three points is a straight line, which is proved as follows: if ABC can form a triangle, then AB+BC is greater than AC, which conflicts with AB+BC=AC, so ABC is in a straight line;

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