a² - 2a + 1 = (2a - 3)²
(a - 1)² = (2a - 3)
(2a - 3 + a - 1)(2a - 3 -a + 1) = 0
(3a - 4)(a - 2) = 0
a = 4/3 或 a = 2
当 a = 4/3 时 2a - 3 = -1/3 < 0 （舍去)
当 a = 2 时 2a - 3 = 1
综上：a = 2