y² = 2px
圆心为坐标原点, 所以A, B关于x轴对称; 二向量相互垂直,所以向量OA与x轴夹角为45˚
A(rcos45˚, rsin45˚), r = 2√2, A(2, 2)
2² = 2p*2, p = 1
y = 2x