Question

VECTORS:
The vectors a b and c are such that a+b+c=0. Determine the value of a•b+a•c+b•c if |a|=1, |b|=2 and |c|=3..
here's my solution: http://sketchtoy.com/57497953

Answer 1

can you please explain why did you do this: a²+b²+c²+2ab+2bc+2ac=0?

Answer 2

@RaphaelFilgueiras

Answer 3

(a+b+c)=0->(a+b+c)dot(a+b+c)=0=|a|²+|b|²+|c|²+2(a.b+b.c+a.c)

Answer 4

a.b is a (dot) b?

Answer 5

yes

Answer 6

yes..

Answer 7

@RaphaelFilgueiras sorry, i still don't understand your method
why did you transform (a+b+c)=0 into (a+b+c)dot(a+b+c)=0 ?? O.o
sorry i'm a slow learner..

Answer 8

just because i want,and i can, zero is orthogonal to any vector, but multiply by itself will lead me to the answer.

Answer 9

you can multiply by anything, but that was a good choice