Question

dn

Answer 1

are you sure you didn't leave anything out?
a·b = |a| |b| cos(θ)
we need to know what a·b is

Answer 2

yep i didn't leave anything

Answer 3

I don't think it can be solved.
a·b is a number, and it can not be found using the fact that a + b + c = 0, because these are just vectors.

Answer 4

you are wrong,it can be solved.

Answer 5

ok, let me know when you found the answer

Answer 6

Think of it as a triangle. Using the cosine rule:

Answer 7

ah I see now