Question

已知二次函数y=x^-(a+2)x-9图像的顶点在y轴上

Answer 1

y=x^2-(a+2)x-9

=[x-(a+2)/2]^2-(a+2)^2/4-9

顶点在y轴上,则顶点横坐标等于0

则(a+2)/2=0

a=-2

y=x^2-9

y=0,x^2=9

x=3,x=-3

所以和x轴的交点坐标是(-3,0)和(3,0)