Question

Giúp mình bài 3 với.

Answer 1

Ta có vector MN=1/2 vectorMA+1/2 vector MC (ct trung điểm)

theo đề ta có 5 vectorMA+9 vectorMB=vector 0=>MA k cùng phương MB=>vector MA=9/14 vector BA

lại có vector MC=vector CB+vector BM=5/14 vectorBA+vector AC+vector BA=19/14 vector BA+vector AC

=>vector MN=1/2(19/14 vector BA+vector AC+9/14 vector BA)=1/2(2vectorBA+vector AC)=vectorBA+1/2vector AC