Question

If B
AxBI= \Ā.BI, then the angle between
A and B will be :
(1) 30°
(3) 60°
(2) 45°
(4) 53
th​

Answer 1

Answer:

We know that,

A×B=ABsinθ

Also, A.B=ABcosθ

Given : ∣A×B∣=

3

A.B

Using ∣A×B∣=∣A∣∣B∣sinθ

We get ∣A×B∣=ABsinθ

A.B=∣A∣∣B∣cosθ

∴ ABsinθ=

3

ABcosθ

tanθ=

3

⟹θ=60

o

Now (A+B)

2

=A

2

+B

2

+2A.B

=A

2

+B

2

+2ABcosθ

=A

2

+B

2

+2AB×

2

1

=A

2

+B

2

+AB

or ∣A+B∣=(A

2

+B

2

+AB)

1/2