math
posted by raja .
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.

let the angle be Ø
by the cosine law
7^2 = 3^2 + 5^2 2(3)(5)cosØ
30cosØ = 9+2549
cosØ = 15/30 = 1/2
Ø = 150°
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