已知抛物线y=x^2 - 1上一定点B(-1,0)和两动点P,Q.当P在抛物线上运动时,BP垂直PQ,则Q的横坐标取值范围是?
參考答案:设P(x1,x1^2-1),Q(x2,x2^2-1),因为垂直,所以斜率乘积为-1,(x2^2-1-x1^2+1)(x1^2-1)/(x2-x1)(x1+1)=-1,x1x2+x1^2-x2-x1=-1,x1^2+(x2-1)x1-x2+1=0,因为x1属于R,所以x2^2-2x2+1+4x2-4>=0,(x2+3)(x2-1)>=0,x2<=-3或x2>=1
