If `A B C D` is a rhombus whose diagonals cut at the origin `O ,` then proved that ` vec O A+ vec O B+ vec O C+ vec O D+ vec Odot`

Explanation

Since the diagonals of a rhombus bisect each other, `vec(OA) = - vec(OC) and vec(OB) = - vec(OD)` and so
`vec(OA) + vec(OB) + vec(OC) + vec(OD) = vec0`.