If ` | vec A| = 2, | vec B| =5 ` and ` | vec A xx vec B | =8 `, din the value of (vec A. vec B0`.

Explanation

We know that ` | vec Axx vec B|^2 + ( vec A.vec B)^2 = A^2 B^2`
or ` (vec A.vec B)^2 = | vec A|^2 | vecB|^2- |vec Axx vec B|^2`
`= (2)^2 (5)^2 - (8)^2 = 100 - 64 = 36`
or ( vec A. vec B) = +- 6`.