Cho 6 điểm A, B, C, D, E, F. Tổng $\overrightarrow {AB} + \overrightarrow {CD} + \overrightarrow {EF}$ bằng:

A. $\overrightarrow {AF} + \overrightarrow {CE} + \overrightarrow {DB}$;

B. $\overrightarrow {AE} + \overrightarrow {CB} + \overrightarrow {DF}$;

C. $\overrightarrow {AD} + \overrightarrow {CF} + \overrightarrow {EB}$;

D. $\overrightarrow {AE} + \overrightarrow {BC} + \overrightarrow {DF}$.

Đáp án đúng là: C.

Ta có: $\overrightarrow {AB} + \overrightarrow {CD} + \overrightarrow {EF}$

$= \overrightarrow {AD} + \overrightarrow {DB} + \overrightarrow {CF} + \overrightarrow {FD} + \overrightarrow {EB} + \overrightarrow {BF}$

$= \overrightarrow {AD} + \overrightarrow {CF} + \overrightarrow {EB} + \left( {\overrightarrow {DB} + \overrightarrow {FD} + \overrightarrow {BF} } \right)$

$= \overrightarrow {AD} + \overrightarrow {CF} + \overrightarrow {EB} + \left( {\overrightarrow {FD} + \overrightarrow {DB} + \overrightarrow {BF} } \right)$

$= \overrightarrow {AD} + \overrightarrow {CF} + \overrightarrow {EB} + \overrightarrow {EF}$

$= \overrightarrow {AD} + \overrightarrow {CF} + \overrightarrow {EB}$.