Question

find the angle between vectors A and B if Mod of vector is equal to 1 and Mod of vector b is equal to 2 and and a cross b is equal to i+j+k​

Answer 1

The angle α which the resultant R makes with A is given by

tanα=

A+Bcosθ

Bsinθ

or

cos(θ/2)

sin(θ/2)

=

A+Bcosθ

2Bsin(θ/2)cos(θ/2)

which gives A+Bcosθ=2Bcos

2

(

2

θ

)

or A+B[2cos

2

(

2

θ

)−1]=2Bcos

2

(

2

θ

)

A=B