Cho hình bình hành ABCDABCDABCD. Đẳng thức nào sau đây SAI?
BD→=BA→+BC→\overset{\rightarrow}{BD} = \overset{\rightarrow}{BA} + \overset{\rightarrow}{BC}BD→=BA→+BC→.
AB→=DC→\overset{\rightarrow}{AB} = \overset{\rightarrow}{DC}AB→=DC→.
AC→=BA→−BC→\overset{\rightarrow}{AC} = \overset{\rightarrow}{BA} - \overset{\rightarrow}{BC}AC→=BA→−BC→.
AC→=AB→+BC→\overset{\rightarrow}{AC} = \overset{\rightarrow}{AB} + \overset{\rightarrow}{BC}AC→=AB→+BC→.
AC→=BA→−BC→\overset{\rightarrow}{AC} = \overset{\rightarrow}{BA} - \overset{\rightarrow}{BC}AC→=BA→−BC→ sai vì BA→−BC→=CA→\overset{\rightarrow}{BA} - \overset{\rightarrow}{BC} = \overset{\rightarrow}{CA}BA→−BC→=CA→.
