If two vectors are equal in magnitude and their resultant is also equal in magnitude to one of them, then the angle between the two vectors is

Options

(a) 60°
(b) 120°
(c) 90°
(d) 0°

Correct Answer:

120°

Explanation:

The angle θ between the vector A and B
Using the cosine rule, R² = A²+B²-2AB cosθ
Where R=A=B, then
R² = R²+R²-2RR cosθ
cosθ = -1/2
θ = 120°.