If `|vec(a)|=2, |vec(b)|=5 and |vec(a)xxvec(b)|`, then what is `vec(a). vec(b)` equal to ?

Options

A. `4`
B. `6`
C. `8`
D. `10`

Answer

B

Explanation

We know that
`|vec(a)xxvec(b)|^(2)+|vec(a).vec(b)|^(2)=|vec(a)|^(2)xx|vec(b)|^(2)`
`:. 64+|vec(a).vec(b)|^(2)=(4xx25)`
`rArr |vec(a).vec(b)|^(2)=36`
`rArr vec(a).vec(b)=6`