cho hình bình hành ABCD tâm O. CMR:
a) \(\overrightarrow{CO}\) - \(\overrightarrow{OB}\) = \(\overrightarrow{BA}\)
b)\(\overrightarrow{AB}\) - \(\overrightarrow{BC}\) = \(\overrightarrow{DB}\)
c)\(\overrightarrow{DA}\) - \(\overrightarrow{DB}\) = \(\overrightarrow{OD}\) - \(\overrightarrow{OC}\)
d)\(\overrightarrow{DA}\) - \(\overrightarrow{DB}\) + \(\overrightarrow{DC}\) = \(\overrightarrow{0}\)