向量DE+向量DF
=1/2向量AC+1/向量2BC
=1/2向量b+1/2(向量AC-向量AB)
=1/2向量b+1/2(向量b-向量a)
=向量b-1/2向量a
向量AD+向量BE+向量CF
=1/2向量AB+1/2向量BC+1/2向量CA
=1/2向量AB+1/2(向量AC-向量AB)+1/2(-向量AC)
=0
也可这样算
向量AD+向量BE+向量CF
=向量AD+向量DF+向量CF
=向量AF+向量CF
=1/2向量AC-1/2向量AC
=0
你把中点位置也该了丫那么::::
向量AD+向量BE+向量CF
=1/2(向量AB+向量AC)+1/2(向量BA+向量BC)+1/2(向量CB+向量CA)
=1/2[(向量AB+向量BA)+(向量AC+向量CA)+(向量BC+向量CB)]
=0