Question

if |a+b| =a•b.What is the angle between a and b.​

Answer 1

Answer:

Let the angle between two vectors AandB be θ

So

|A+B|2=|A|2+|B|2+2|A||B|cosθ

Again

|A−B|2=|A|2+|B|2+2|A||B|cos(180−θ)

By the given condition

|A+B|=|A−B|

So

cosθ=cos(180−θ)

⇒θ=180−θ

⇒θ=90∘