hi

I've tried to solve a problem which is saying that I've A,B and C are 3 vectors in R^3 and has a magnitude of 2 such that a+b+c=0 find the value of (a.b)+(b.c)+(a.c)

first, A+B= -c

so (A+B).C= 2 * 2* cos 180 = -4

So A.C + B.C= -4

and I've do so for A+c=-b

so i got (A.b)+(b.c)= -4

and I found that (A.B)= (A.C) i.e the angle between A and B is the same as the angle btwen A and C

Anyway I can't go on from here. If that's right how can i get the last result . and if not .. please, tell me what is wrong