The given quadratic equation is 4y^2 - 4y + 1 = 0, which factors into the perfect square (2y - 1)^2 = 0. Taking the square root of both sides gives 2y - 1 = 0, meaning y = 1/2 is a double root. Since both roots are equal to 1/2, their difference is 1/2 - 1/2 = 0.