If two vectors are equal in magnitude and their resultant is also equal in magnitude

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°.

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