,(2)已知二次函数y=ax2+c ,当x取x1,x2(x1x2, x1,x2分别是A,B两点的横坐标)时,函数值相等, 则当x取x1+x2时,函数值为 ( )A. a+c B. a-c C. c D. c,D,大显身手,大显身手,(1)已知二次函数y=3x2+4,点A(x1,y1), B(x2,y2), C(x3,y3), D(x4,y4)在其图象上,且x2|x1|, |x3|x4|, 则 ( ),x1,x2,x3,x4,y1,y4,y3,y2,A.y1y2y3y4,B.y2y1y3y4,C.y3y2y4y1,D.y4y2y3y1,B,