Question

The resultant of vectors P and Q is perpendicular to vector P also vector P=R, the angle between vectors
P and Q is:
a) 45°
b) 135°
c)225°​

Answer 1

Answer:

P⃗ ⋅(P⃗ +Q⃗ )=0  

⟹P2+PQcosθ=0

⟹cosθ=−PQ

⟹θ=arccos(−PQ)