Question

If resultant of two unit vectors is a unit vector, then find angle between them.
(A) 30°
(B) 60°
(C) 90°
(D) 120​

Answer 1

Answer:

Correct option is

B

3,120∘

∣a+b∣=1

∣a∣2+∣b∣2+2∣a∣∣b∣cosθ=1

→2(1+cosθ)=1

→cosθ=2−1θ=120∘

∣a+b∣=∣a∣+∣b∣2−2∣a∣∣b∣cosθ

=1+1−2cos120∘

=2+2×21=3.