If veca and vecb are two unit vectors in...

If `veca and vecb` are two unit vectors inclined at an angle `pi//3 then { veca xx (vecb+veca xx vecb)} .vecb` is equal to

A

`(-3)/4`

B

`1/4`

C

`3/4`

D

`1/2`

Text Solution

Verified by Experts

The correct Answer is:

a

` { veca xx (vecb + veca xx vecb)} .vecb`
` { veca xx vecb + veca xx (veca xx vecb)} .vecb`
`= [veca vecb vecb] = {( veca.vecb) veca - (veca .veca) (vecb.vecb)`
` cos^(2) pi/3 -1 = -3/4`

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