y
= x² - 2x - 3
= (x - 1)² - 4
顶点坐标 (1 ,-4)
对称轴是 x = 1
当 x = 0 时 ,y = -3
所以与y轴交点是 (0 ,-3)
当 y = 0 时 x² - 2x - 3 = 0
(x + 1)(x - 3) = 0
x = -1 或 x = 3
所以与x轴交点是 (-1 ,0) 和 (3 ,0)