✔ 最佳答案
1) OA=i,OB=j, CD=r, BE=s
OE=(1+s)J, AE=OE-OA=-i+(1+s)j
BD=(1+r)i, OD=OB+BD=(1+r)i+j
AE.OD=-(1+r)+(1+s)=s-r
2(a) AF:FE=1:4
OF=(4OA+OE)/5=(4/5)i+[(1+s)/5]j
(b) OF=kOD=k(1+r)i+kj
(c) Since AE.OD=0;s-r=0=>r=s
Also k(1+r)=4/5 and k=(1+s)/5 =>
(1+s)(1+s)/5=4/5
s=r=1 and k=2/5