Question

if vectors a+b+c=0 and modulus of the vectors a, b and c are 3 ,5 and 7 respectively. find the angle between the vectors a and b.

Answer 1

let the angle be Ø

by the cosine law

7^2 = 3^2 + 5^2 -2(3)(5)cosØ
30cosØ = 9+25-49
cosØ = -15/30 = -1/2
Ø = 150°