题目

已知平面上有三点A(1，－a)，B(2，a2)，C(3，a3)共线，则实数a＝. 答案：【解析】∵＝(1，a2＋a)，＝(1，a3－a2)， 又∵A、B、C三点共线，∴∥， ∴1×(a3－a2)－(a2＋a)×1＝0，即a3－2a2－a＝0， ∴a＝0或a＝1±. 答案：0或1±(2014·山西省六所重点中学模拟)—Believe it or not，my sister and I are twins.—Oh，you must have had the case________you were taken for your sister.A．which　B．whoseC．where　D．whom