因为对称轴 x = 2所以设抛物线的解析式y = a(x - 2)² + h把 (1 ,0) 和 (0 ,-3) 代入得 :a + h = 04a + h = -3解得：a = -1h = 1所以 y = -(x - 2)² + 1 ,即 y = -x² + 4x - 3...