Question

If |A+BI=|AI=IB, then the angle between A & B and is :
(A) 0°
(B) 60°
(C) 90°(D) 120​

Answer 1

Explanation:

Let the angle between two vectors  

A  and  B  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 ,

cos θ = cos ( 180 − θ )  

⇒ θ = 180 − θ

⇒ θ = 90 ∘