`ABCDEF` is a regular hexagon, Fig. 2 (c ) .65. What is the value of
` (vec (AB) + vec (AC) + vec (AD) + vec (AE) + vec (AF) ?`
.

Explanation

` vec (AB) + vec (AC) + vec (AE) + vec (AF)`
`= vec (AB) + vec (AD) + vec (DC) + vec (AD) + vec (AD) + vec (DE) + vec (AF)`
`= 3 vec (AD) + vec (AB) + vec (DE) + vec (DC) + vec (AF) =3 vec (AD)`
`=- 3 (vec 2 (AO) =6 vec (6 DE)`
[:. vec (AB) =- vec (DE), and vec (DC) =- vec (AF)]`.