... Ba i 14 a) VN 4: Chng minh ba im thng hng Hai im trựng uuu chng minh ba im A, B, C thng hng ta chng minh ba im ú tho ng r uuu r thc AB = k AC , vi k chng minh hai im M, N trựng ta chng minh ... r uu r uur r Ba i Cho ABC Hai im I, J c xỏc nh bi: IA + 3IC = , JA + JB + 3JC = Chng minh im I, J, B thng hng r r uuu r uuu r uuu uuu r r Ba i Cho ABC Hai im M, N c xỏc nh bi: 3MA + MB = , NB ... im I tho IA + 3IB IC = b) Chng minh ng thng MN luụn i qua mt uuuu cuuu uuu uuur im nh r r r Ba i 19 Cho tam giỏc ABC Cỏc im M, N tho MN = MA MB + MC uu uu uu r r r r a) Tỡm im I cho IA IB...