Question

一.如图C-2-2,已知G1.G2分别是△A1B1C1与△A2B2C2的重心,且向量A1A2=e1,向量B1B2=e2,

Answer 1

设一定点为O

OG1＝（OA1＋OB1＋OC1)/3

OG2＝（OA2＋OB2＋OC2)/3

G1G2=OG2-OG1＝（OA2＋OB2＋OC2)/3-（OA1＋OB1＋OC1)/3

=(A1A2+B1B2+C1C2)/3

=(e1+e2+e3)/3

AB=(-19,-15)

F1*AB=-19-30=-49

F2*AB=-76-75=-151

F1+F2=4i+5j+i+2j=5i+7j

(F1+F2)*AB=-95-105=-200