设切点为(c,d)d = 3c + 1y = x³ - ay' = 3x²在x = c处的斜率 = 切线斜率y'|(x=c) = 3c² = 3c² = 1c = 1 或 -1当c = 1,d = 3 + 1 = 4代入曲线：4 = 1³ - a => a = -3当c = -1,d = 3(-1) + 1...