抛物线y = x 2 –4x + 5 = (x - 2) 2 + 1,即(x - 2) 2 = y – 1,令x’ = x – 2 和 y’= y – 1,可得(x’) 2 = y’,准线方程为y’ = -1/4,所以原抛物线的准线方程为 y – 1 = -1/4,即y = 3/4 .