Find the scalar product of the following pairs of vectors and the angle between them. `2hati-3hatj+6hatk` and `2hati-3hatj-5hatk`

Explanation

Let `veca = 2hati-3hatj+6hatk, vecb = 2hati-3hatj-5hatk`
Then `|veca| = sqrt(4+9+36) = 7`
`|vecb| = sqrt(4+9+25) = sqrt(38)`
`veca.vecb = 4+9-30 = -17`
If `theta` is the angle between `veca` and `vecb` then
`theta = cos^(-1) ((veca.vecb)/(|veca||vecb|)) = cos^(-1) ((-17)/(7sqrt(38)))`.