d) vecto DA- vecto DB+ vecto DC= vecto 0

d) Theo chứng minh trên ta có: $\overrightarrow{\text{DA}}$ – $\overrightarrow{\text{DB}}$ = $\overrightarrow{BA}$= $\overrightarrow{CD}$

⇒ $\overrightarrow{\text{DA}}-\overrightarrow{\text{DB}}+\overrightarrow{\text{DC}}$ = $\overrightarrow{\text{CD}}$ + $\overrightarrow{DC}$ = $\overrightarrow{0}$.

Vậy $\overrightarrow{\text{DA}}-\overrightarrow{\text{DB}}+\overrightarrow{\text{DC}}$=$\overrightarrow{0}$.