Question

已知A(-1,-4),B(8, ),且A、B、C三点共线,则C点的坐标为(    )

A.(9,1)             B.(-9,1)              C.(9,-1)          D.(-9,-1)

Answer 1

解析：设C(x,y),=(8, )-(-1,-4)=(9,),

=(x,y)-(8,)=(x-8,y-),

=(x,y)-(-1,-4)=(x+1,y+4),

∵A、B、C三点共线,

∴与与三个向量共线.

∴

经检验x=9,y=1适合.

答案：A