cho 6 điểm A, B, C, D, E, F. cm:
a, vectơ AB+ vectơ DC= vectơ AC+ vectơ DB.
b, vectơ AD+ vectơ BE+ vectơ CF= vectơ AE+ vectơ BF+ vectơ CD
cho 6 điểm A, B, C, D, E, F. cm:
a, vectơ AB+ vectơ DC= vectơ AC+ vectơ DB.
b, vectơ AD+ vectơ BE+ vectơ CF= vectơ AE+ vectơ BF+ vectơ CD
a.vectơ AB+ vectơ DC= vectơ AC+ vectơ DB
VT:AB+DC=(AC+CB)+(DB+BC)
=AC+CB+DB+BC
=AC+DB+(CB+BC)
=AC+DB+0
=AC+DB=VP (đpcm)
b.vectơ AD+ vectơ BE+ vectơ CF= vectơ AE+ vectơ BF+ vectơ CD
VT:AD+BE+CF=(AE+ED)+(BF+EF)+(CF+FD)
=AE+ED+CF+(ED+EF+FD)
=AE+ED+CF+0
=AE+ED+CF=VP (đpcm)
———————–Nguyễn Hoạt————————–