Find a unit vector parallel to the sum of the vector `(hati + hatj + hatk)` and `(2hati - 3hatj + 5hatk)`.

Explanation

Let `veca = (hati hatj + hatk)` and `vecb = (2hati - 3hatk + 5hatk)`. Then,
`(veca+vecb) = (hati + hatj + hatk) + (2hati - 3hatj + 5hatk) = (3hati - 2hatj + 6hatk)`
Required unit vectors parallel to `(veca + vecb)` are
`+-((3hati - 2hatj + 6hatk))/(sqrt(3^(2) + (-2)^(2) + 6^(2))) = +- 1/7(3hati - 2hatj + 6hatk)`.