It is known that b+c=-a, c+a=-b, and a+b =-c; Because abc is not equal to 0, that is, any one of A, B and C is not equal to 0 and can be used as the denominator, so we can get A2/(-A)+B2/(-B)+C2/(-C) =-(A+B+C) through substitution simplification.

The result is 0.