Lời giải:
\(\overrightarrow{AB}-\overrightarrow{DC}+\overrightarrow{BC}-\overrightarrow{AD}=(\overrightarrow{AD}+\overrightarrow{DB})-(\overrightarrow{DB}+\overrightarrow{BC})+\overrightarrow{BC}-\overrightarrow{AD}\)
\(=\overrightarrow{AD}+\overrightarrow{DB}-\overrightarrow{DB}-\overrightarrow{BC}+\overrightarrow{BC}-\overrightarrow{AD}\)
\(=\overrightarrow{0}\)