If `veca, vecb and vecc` are three unit vectors such that `veca xx (vecb xx vecc) = 1/2 vecb , " then " ( vecb and vecc ` being non parallel)

Options

A. angle between `veca and vecb is pi//3`
B. angle between `veca and vecc is pi//3`
C. angle between `veca and vecb is pi//2`
D. angle between `veca and vecc is pi//2`

Answer

b,c

Explanation

`vecaxx (vecb xxvecc) = 1/2 vecb`
`or (veca.vecc) vecb - (veca .vecb) vecc= 1/2 vecb`
` Rightarrow veca.vecc = 1/2 and veca.vecb=0`
` Rightarrow 1.1 cos alpha = 1/2 and veca bot vecb`
` Rightarrow alpha= pi/3 and veca bot vecb`