|m|=2,|n|=sqrt(3),m·n=(2,0)·(3/2,√3/2)=3
AD=(AB+AC)/2=(2m+2n+2m-6n)/2
=2m-2n
故:|AD|^2=4(|m|^2+|n|^2-2m·n)
=4(4+3-2*3)=4,即:|AD|=2
|m|=2,|n|=sqrt(3),m·n=(2,0)·(3/2,√3/2)=3
AD=(AB+AC)/2=(2m+2n+2m-6n)/2
=2m-2n
故:|AD|^2=4(|m|^2+|n|^2-2m·n)
=4(4+3-2*3)=4,即:|AD|=2