题目内容：

Y.如图,抛物线y=1/2x2_x+a与x轴交于A,B两点,与y轴交于点C,其顶点在直线y=_2x上.

优质解答

1.顶点:x=1y==a-1/2∵y=-2x∴a-1/2=-2a=-3/22.y=1/2x²-x-3/2则1/2x²-x-3/2=0x=-1,3交点(-1,0)(3,0)3.C(0,-3/2)D(2,3/2)D'(2,-3/2)∵y=1/2x²-x-3/2左边=右边=-3/2∴D'在抛物线上