If `veca` and `vecb` are unit vectors represented by the adjacent sides of a regular hexagon, taken in order, what are the vectors represented by the other sides taken in order?

Explanation

Let `vec(AB)` = `veca, vec(BC)` = `vecb`
`implies vec(AC)` = `veca+vecb`
`vec(AD)` = `2vec(BC)`= `2vecb` (therefore `vec(AD)` is parallel to `vec(BC)` and twice of `vec(BC)`)
therefore `vec(CD)` = `vec(AD)-vec(AC)` = `2vecb-(veca+vecb)` = `vecb-veca`
`vec(DE)` = `-veca`
`vec(EF)` = `-vecb`
`vec(FA)` = `-vec(CD)` = `veca-vecb`.