If ` vec a` and vec b` are two non collinerar unit vectors and if ` | vec a+ vec b | = sqrt 3`, then find the value of ` (vec a-vec b). (2 vec a+ vec b)`.

Explanation

Given ` a= b= 1` and ` | vec a + vec b| = sqrt 2`
:. ` a^2 +b^1+ 2 ab cos theta =3 ` or ` cos thete = 1//2`
Now ( `vec a-vec b`). (` 2 vec a+vec b`)= `2 a^2 -b^2 - ab cos theta`
= 2- 1 1/2 1/2` .